A slow cooker is great for slow cooker meatballs in a tomato sauce, then you can just do spaghetti and some green veg or salad to go with it. It doesn't taste 'slow cooked' so to speak.
Meatloaf is easy to make in advance and it freezes well in slices or make it in mini loaf tins and freeze. It reheats well and goes with new potatoes or mash and green beans or broccoli and carrots. You can add gravy if you like it.
Falafel (you can buy them ready made), hummus, olives, green salad, cherry tomatoes, cucumber and pita breads.
Cauliflower & broccoli cheese, sausages and mini jacket potatoes, boiled new potatoes, or wedges. You can add other veg to the cauliflower cheese and to macaroni cheese such as cubed carrot, fried mushrooms, sweet corn etc (or cheat and use frozen mixed veg).
Welsh rarebit with a fried egg on top (Buck rarebit) or you could poach the egg, serve with a big salad. This is really quick and tasty for a treat.
Cook some salmon whilst you boil pasta, chuck some small florets of broccoli (or peas) in the pasta midway through cooking, flake the cooked salmon, & drain the pasta and broccoli. Chuck the salmon & drained pasta/broccoli back in the pan on low heat with some half fat creme fraiche, gently stir through, add a handful of grated parmesan, season with black pepper and seasoning salt (Herbamare is nice), serve topped with a little more parmesan and some cooked vegetables (asparagus is nice) or salad.
Chicken satay skewers are easy to make, serve with rice and roasted veg. Coconut rice goes really well with this.