Here are a couple different casseroles that my family loves. 
Chile Chicken Casserole
1 T. olive oil
1 lrg. onion, chopped (about 1 cup)
1 medium bell pepper, chopped (your choice as to color)
1 clove garlic, finely chopped or minced
3 cups diced or shredded cooked chicken
3 cups cooked white rice
2 cups sour cream (1 16 oz. carton)
2 cups cooked black eyed peas (canned) drained
-OR-
2 cups cooked black beans (canned) drained
1 cup small curd cottage cheese
2-4 cups shredded cheddar cheese (depending on how "cheesy" you want it.)
2 cans (4oz.) diced green chilis (be CAREFUL not to buy diced jalapenos...the cans look very similar)
Heat oven to 375. Grease a 13x9 or 3 qt. casserole dish. Heat oil in dutch oven over medium heat. Cook onion, bell pepper, and garlic in oil, stirring frequently, until crisp-tender, remove from heat. Stir in remaining ingredients except cheese and chilis.
Spread half of the chicken mixture in baking dish: sprinkle with 1/2 of cheddar & chilis. Make another layer and top with remaining cheese. 
Bake uncovered 25 to 30 min or until heated through. Even better re-heated the next day. 
ENJOY!!!
Cheddar Chicken Spaghetti
1 8oz. package spaghetti --broken
2 cups cooked chicken --cubed
1 cup shredded cheddar cheese
1 cup shredded swiss cheese
1 can cream of chicken soup -- undiluted
1 cup milk
2 heaping tablespoons Mayo
1 roasted red pepper (from the jar) --diced
1/4 cup onions --finely diced
1/2 t. garlic powder
1/2 t. salt 
1/2 t. pepper
1/2 t. dried basil (you could probably use fresh but I have not)
In a small skillet, saute' onion until soft but not mushy. Cook spaghetti until desired doneness. Combine everything except the cheddar cheese in a large bowl. Add the cooked spaghetti and toss to coat. Transfer to a greased 13x9 baking dish. Sprinkle with the cheddar cheese. Bake at 350 20-25 min. until heated through.