When pressed for time or getting home late I have done these with success:
Irish Stew (chunky canned soup) with a microwaved cut potato added, plus an onion.

Aside from softening/heating the potato, the heating of the soup is almost set-and-forget, leaves just one thing to clean plus your bowl (unless you want to eat it 'cowboy style').

:p

That's obviously a winter option and the soups are great for taking in leftovers like veg or meats in the fridge.

Good suggestions in the posts above, about pre-cooking some meats for use over three days.

Keeping it basic and fresh usually means a satisfying meal. Not necessarily with lots of time, effort or cleaning. Possibly a lot fewer calories, additives and fats than eating fast food, too.

Mrs BamaVol has always said that without me, she'd survive off grocery store salad bars.

I enjoy cooking enough to do it even if I'm the only one I'm feeding.

When I was really broke, I'd dress up a can of black beans with additives like Rotel, a sauteed onion, a can of corn or whatever I had on hand and serve over rice.

Today if short on time, I can still throw a salad together in 5 minutes and always have the basic ingredients on hand.

In my family, the default quick-n-cheap dinner was ground beef, chopped onion, and canned green beans simmered in tomato sauce. Surprising how filling that could be :)

Substitute elbow macaroni for the green beans and you have one of Grandma BamaVol's depression-era specialties. At the school cafeteria, it was called American Goulash. Her other depression food was a bowl of ritz crackers covered in warm milk. <shudder>