Mexican Chicken Casserole with Tortilla Chips

Ingredients

• 2 cups chicken leftover, about 2 chicken breasts fully cooked and chopped
• 1/2 pound tortilla chips
• 2 cups cheddar cheese grated
• 15 ounces tomatillos canned, drained and diced
• 1/2 red pepper diced, optional
• 1/4 cup button mushrooms diced, optional
• 3 ounces chipotles in adobo sauce about half a 6.5 ounce can
• 10 ounces cheddar cheese soup canned
• 1 medium onion peeled and halved
• 2 garlic cloves
• 1 tablespoon milk
• salt
• pepper