Chicken Spaghetti

1 medium onion, chopped
1 medium bell pepper, chopped
3 tablespoons butter
1 roasted deli chicken, deboned and diced
1 (10 3/4 ounce) can cream of mushroom soup
1 (10 3/4 ounce) can cream of celery soup
1 (2 ounce) jar pimiento, drained
1 (2 1/2 ounce) jar sliced mushrooms, drained
1/2 (6 ounce) can black pitted olives, drained and chopped
1 (16 ounce) package long spaghetti, cooked
1 teaspoon salt
1/2 teaspoon pepper
1 cup grated Cheddar cheese

Heat the oven to 375 degrees F.

Saute onion and bell pepper in butter. Add the soups, pimientos, mushrooms, chicken, olives and spaghetti. Season with the seasonings. Put the mixture into a large casserole dish. Top with cheddar cheese. Bake for 45 minutes, or until cheese is melted.