I make a pasta dish with leftover roast chicken and spinach.
Layer of steamed frozen spinach, layer of chicken pieces, layer of pasta shapes (twists usually) in a homemade tomato sauce then a layer of grated mozzarella and in the oven till the cheese is melty and browned.
I also make a sort of biryani-esque rice dish
In a heavy bottomed deep but shallow pan with a lid - Chop an onion finely, sweat till translucent and even a wee bit browned at edges, add a tablespoon of curry paste, add basmati rice to cover the bottom of the pan and the chicken chopped up, add boiling water (twice as much as the rice I usually use a cup of rice/2 cups water) a handful of frozen peas/green beans or whatever and cook with a lid on until the rice is done. We usually have chapattis with it.
I have also made chicken and mushroom pie similar to above with a sauce made from leftover gravy, some fresh thyme and a tablespoon or two of creme fraiche and rough puff pastry.
I make other ricey things with different kinds of rice like using paella rice and smoked paprika to make a kind of paella-ish thing with peppers and peas in or we have oven baked risotto occasionally.