Chicken Spaghetti casserole

•  8 oz uncooked spaghetti, broken into 3 in pieces
• 3 c cubed chicken, cooked (could use rotisserie chicken if desired)
• 10 3/4 oz cream of chicken soup (I usually make my own gf)
• 1 c milk
• onion
• 1 C cheddar cheese 
• 1 C swiss cheese, divided
• 4 oz mushrooms
• 1/2 c chopped roasted sweet red peppers (this is the best part, we just used fresh red peppers)
• 3 T mayonaise
• 1 1/2 t steak seasoning (salt, pepper, garlic, onion powder, paprika)
• 1/2 t dried basil

1. Cook spaghetti according to package directions. 
2. Combine in large bowl: chicken, soup, milk, onion, 1/2 cup cheddar, 1/2 c swiss, mushrooms, peppers, mayo, steak seasoning, basil
3. Drain spaghetti and add to chicken mixture. Transfer to 13x9 pan. Cover and bake at 350 degrees for 20 minutes. Uncover, sprinkle with remaining cheeses. Bake until heated through and cheese is melted, 5-10 minutes longer.