Easily: leftovers. Literally just cook on sunday. Takes like 1.5-2hrs. Make 10-12 servings. Dinner for 2 for 5-6 days. Eat it all week.

I have done this every week for my entire adult life and have never spent more than like 2hrs per week cooking unless I wanted to make something particularly difficult for fun.

Also, you can make big batches of stuff to freeze or can. Canning is easy: get a pressure cooker, buy some big mason jars - they're cheap and reusable, look up the pressure and time requirements (especially if the dish contains meat), and boom. Shelf stable food you can store in the pantry and eat whenever.

Meal prep ideas:

Spend like 3hrs making 10 dozen pierogies (potato & cheese and pork & mushroom & sauerkraut are my favorites), freeze half & boil/pan fry whenever. Eat the rest for the week with some sauerkraut or cucumber dill salad (umborksalat) as a side. Costs maybe 30 bucks for everything and makes food for 2 weeks (6 pierogies per serving). Make more if you want - it doesn't take much extra time.

Chinese style dumplings are the same as pierogies but with square wrappers and more ingredients. Buy wonton wrappers. Make filling with ground pork, garlic, green onion, msg, ginger, salt, pepper, soy sauce, vinegar. Add napa cabbage if you want to stretch the filling. Fill wonton wrappers. Make however many you want. Takes a few hours if you're gonna make a shitload, but it is easy - pop on a movie and make hundreds if you want. Freeze and boil whenever. Or make potstickers by heating oil in a pan, putting in fresh or frozen dumplings, cooking for a bit before adding some water before immediately covering with a lid. Cook a bit and they should release from the pan - scrape them up with a spatula if they don't.

Get a very large pot. Make a full pot of gumbo, red beans and sausage for red beans & rice, or split pea soup. You can make gallons of these very cheaply in the same time it'd take to make a smaller quantity. Freeze or can most of it. Cook rice for the week for gumbo or red beans and rice (20mins on the stove, 2mins of prep). Serve over rice (don't serve split pea soup over rice unless you're a psychopath). Done.

Make west african peanut soup. Made of sweet potatoes, peanut butter, chicken if you want, collard greens, tomatoes. Fucking delicious. Very filling and calorie dense. Like 25 bucks for a week of delicious soup. I make like 2kg when I do this. Could double batch and freeze/can half as well.

Jambalaya/jollof rice/other similar rice dishes. Make 10-12 servings for the week or double it and freeze half.

Lasagna or other pasta bake dishes. Make one dish for the week. Make another to freeze and pop in the oven to cook whenever. Serve with a quick salad.

Enchiladas. Same as pasta dishes (can freeze and cook later). Cook meat/other filling. Heat up a bunch of corn torrillas. Fill with filling. Put into a rectangular casserole dish with some enchilada sauce. Top with enchilada sauce and some cheese. Boom. 12 enchiladas - enough for a week. Especially if you make some cilantro-lime or 'spanish' rice to go with it (rice, boullion, onion, tomato paste, diced tomato, garlic, little oil, water) - throw it all in a pot, simmer 20mins, refrigerate, eat all week as a side dish. Maybe use canned refried beans as a side too.

Tacos. Shred up a rotisserie chicken. Pan fry with onions, garlic, peppers if you want (chipotles in adobo are my favorite. You could use salsa instead or jalapenos or whatever). Boom. Freeze or refrigerate. Heat up and put in tortillas whenever with some fresh cilantro/onion/hot sauce. Make rice as with enchiladas. Can serve with beans, too.