Can one eat a balanced diet if one only cooks once a week?

The types of foods that reheat well are also quite suitable for being balanced in one main dish. Generally speaking, dishes with stuff in sauce freeze/chill and reheat well. So stew, curry, chilli, ratatouille etc. should work. Any of those can be made with plenty of veg, which is important if you're aiming for a balanced diet. An accompanying carbohydrate side can often be cooked in a similar time to reheating the main dish, so this doesn't need to be included (unless you want to of course). From the point of view of sticking to nutritional guidelines you can do much better this way than buying ready prepared stuff, and cheaper.

Freezing in single portions is important; I tend to use containers intended for takeaway meals. Freezing means after 2 or 3 sessions of cooking you've got a variety of meals. I tend to defrost in the fridge, allowing 24 hours.

Personally I batch cook about 5-6 portions most Sundays, but don't rely on reheating these every night. Quick simple meals (like a stir fry or an omelette) add a nice variety.

Yes - this process is often called "Meal Prepping".

Typically with Meal Prepping, you would prepare and cook dinner for the rest of the week - either by cooking something that can be portioned out into individual servings (chili, soup, casserole, crock pot meal, enchiladas, etc), or by cooking multiple portions of the same meal (chicken with rice and vegetables, etc).

There are entire cook books dedicated to meal prepping! Here's just one example:

The Healthy Meal Prep Cookbook

For breakfast and lunch, meal preppers often take easy and quick items that can be portioned out for the week. Such as cheese cut into cubes, baby carrot sticks, hard boiled eggs, yogurt, grapes, crackers, etc.

One caveat that derails people from their meal prepping plans is the monotony of eating the same thing every day for a week. If this happens to you, maybe try food prepping twice a week, and prepare fewer meals. This way you can get a variety of food items, and keep a better variety of nutrients in your system.

For storage, I personally use the RubberMaid Brilliance collection. They have locking covers, can stack easily, are dishwasher safe (I'm lazy), and come in a variety of shapes and sizes - including "Bento" box style, and salad prep style.

Meal prepping can be a lot of fun, can be very healthy, and can save a lot of time!

I recommend a mix. Batch your sauces, soups, and protein. Put some in the fridge and the rest in the freezer. I will make noodles, cold sandwich, and salad fresh.

Chili and chicken thigh are my go to. On chicken thigh I crook with skin on and then remove the skin when cooked. Boiled eggs work on salad and as a snack.

I also clean the vegetables. You can get like 4 days in the fridge. You can get a week on some fruit like oranges.

There are a few very important key things to do, but yes it's generally possible. With some practice, it's even less wasteful (though not at first probably), and some could argue time-saving.

So, the first real problem to tackle is storage. You don't really want to store things in plastic containers. You want to favor glass or pyrex (soda ash) with a good sealable (plastic works well here) lid. Generally, you should avoid Rubbermaid or Tupperware plastic containers. If you do want to use plastic get the disposable kind. The main reason is strongly caustic foods (like tomato sauce) tend to "melt into" the plastic making them hard to clean, and very hard to remove that taste. Using glass, even if it has a plastic lid, removes that problem. As do disposable solutions, but those make a lot of waste.

Next is going to be storage. This is tricky. Avoid the freezer for foods that separate. Normally this is foods that have fruits or high water content. Honestly I never freeze (preference) but that limits me to about 4-5 days. If you freeze you can get longer (weeks I suppose), but I hate when the act of freezing changes the flavor of the food. Do not store at room temperature. At best you will get a day or two, and that can be pushing it.

Labeling is very important. You should label what the food is and most importantly when it was cooked.

Store like foods together. For example, if you make a ton of Penne (just the noodles) store the 10 pounds of pasta together. In one bowl. Save the mixing it in with the sauce for later.

You will have to experiment a bit for this one, but try to stick with foods that have simple textures. You don't want to store food that isn't right if it's a bit too soggy, or that is nasty if it's a bit too crispy. Instead things like corn, green beans, peas, chicken thigh or breast. Things that don't rely on texture much. Conversely, don't try anything that has a texture that needs to be just right. I find that sauces, soups, and stews work well. Crisp foods like salad do not.

Finally, for your own sanity. Don't stop eating out. It's easy to rely on the pre-made meals, but that means you miss out on relaxing or taking a break from the sameness.