Preheat oven to 350F, cook onion, pepper and garlic in a skillet. Transfer to a bowl and add the rest of the ingredients except the chicken, chips and cheese, mix until combined. Spread 1/2 cup of sauce mixture into a dish then layer the chicken, cheese and doritos.
Repeat layers then bake, uncovered, at 350°F for 30 minutes. Increase oven temperature to 400°F* and bake an additional 5 to 10 minutes until bubbly and golden crisp.