Ahhh, a question I am actually qualified to answer!
Exhausted but I can wait to eat:
Baked potatoes or sweet potatoes topped with things. Chili is good. Depending on your dietary standards, it can be the el cheapo canned chili, or the fancy organic low fat canned chili, or chili you have lovingly made and frozen yourself. Or shredded cheese and steamed vegetables. Or frozen veggies with cheese sauce (not that I am admitting to anything...). Or tuna salad. Or chopped meat w. barbeque sauce and cheese. Etc.
Exhausted and I want to eat now:
Scrambled eggs, toast, a piece of fruit (or applesauce)
Oats, yogurt, fruit (chopped fresh or dried), nuts--let it sit so the oats soften. You may need to add a little milk if it's Greek yogurt.
If you have a waffle iron, waffles for dinner--from a box mix or scratch, depending on your standards, with fruit and low-fat sausage or bacon on the side. I think this is less fussy than pancakes myself. Or batter for a Dutch baby (oven-baked pancake) is quick to mix in the blender. (This is not so healthy, though, there's a lot of butter involved.)
Defrost frozen rice or quinoa (or again, if you have more time, rice in the rice cooker) or make couscous. Top according to a "theme"--beans, cheese, salsa and sour cream for Mexican, spaghetti sauce, cheese and whatever meat you have around for Italian, feta, lemon juice, yogurt, plus protein for "greek," etc.
Quesadillas to be filled with whatever's around.
Mix a can of tuna, can of rinsed black beans, chopped onion, salt and pepper, and lots of balsamic vinegar. If you have any salad friendly veggies around (like bell peppers) you can chop them up to go in there too.
Soup from a box or the freezer, depending, plus cheese melted on toast (a little mustard spread on the bread is tasty) and then fruit or cut up veggies on the side.
You can either throw veggies into these, or do super simple sides, which could include
--sliced cucumber in vinegar, or tossed in sour cream and dill
--cut up tomatoes w. balsamic vinegar
--sauteed greens (amount of prep work you do vs. buying bagged up to you)
--roasted veggies. I like asparagus this way when it's in season
etc.
Three cookbook suggestions--
The Make It Fast, Cook it Slow cookbooks (there are two, the first is better)--slow cooker recipes that hit a nice balance between not too many prepared products and not too much prep required)
The Express Lane Cookbooks by Sarah Fritschner from the 1990s (warning, at least the vegetarian version is heavy on the carbs)
Mark Bittman's Kitchen Express cookbook. Very few measurements and the recipes (no more than a paragraph long each) don't take a lot of time, although sometimes they require "pantry" items that only a foodie would consider staples.