I have an old farmhouse recipe book from the 1950's- cheap and cheerful, and maybe at times strange dishes, but I like experimenting!! One from the book, that I like is mashed potato, mixed with leftover cooked meat, and diced onion. Mix in a little gravy, put in ovenproof dish, and put in oven 25-30 mins until thoroughly warmed. Just add veg, and more gravy if wanted. Quick and easy.
Also do a pie base, layer with cooked bacon, chopped up. Then crack 5 eggs on top, top with pastry, and cook. I like this with baked beans
Now the nights are drawing in, I tend to make casseroles or stews, one day, and then they just need reheating the following evening.