Creamed Chicken and Biscuits Casserole

Ingredients

• 1 small onion
• 1 1⁄2 teaspoons butter
• 2 lbs chopped cooked chicken breasts or 2 lbs boneless skinless chicken thighs
• 1 (10 3/4 ounce) can cream of chicken soup
• 1⁄2 cup mayonnaise
• 1 cup milk
• 1⁄2 cup chopped pimiento or 1⁄2 cup sauteed red bell peppers or 1⁄2 cup jarred roasted red pepper
• 1 1⁄2 cups shredded mild cheddar cheese
• refrigerated biscuit