My boyfriend comes home quite late sometimes, meaning that I'll eat dinner at 7, and he'll be having his dinner at 10 or 11 if not later.
I either make dishes that can be reheated, such as stews, chilli con carne, bolognese, lasagne, osso buco and so on, and then cook rice, pasta or potatoes for mash when it's time to eat. For reheating, a microwave is really useful.
Or I make a salad, alternatively have the different ingredients in different bowls to avoid some things getting soggy.
Or we have sandwiches or just bread with cheese/ham/whatever.
Or just make something that can be eaten cold or hot, such as pizza. A cold piece of omelette on a piece of toasted rye bread is also quite nice.
Sometimes there are parts of a meal that can be made ahead and then parts that just need to be fried, which will take a couple of minutes. For example if I'm having this dish: Smoky paprika salmon with avocado, tomato & jalapeño salad I'll make the salad for when I want to eat, as well as cooking one piece of salmon. When done with my dinner, I'll put the salad in the fridge, and when my boyfriend comes home, I'll take it out as well as cook a piece of salmon for him.
I'm often cooking a whole chicken in the oven, then having a leg (hot) with my dinner. The cold leftovers are nice in sandwiches, in salads, in a simple curry sauce with rice (like a colonial curry).