Heat oven to 400. Grease a 9-inch pie plate. Mix chicken, onion and seasoning mix. Sprinkle in plate. Stir baking mix, milk and eggs with fork until blended. Pour into plate. Bake 30 to35 mins. Sprinkle with cheese. Bake 1 to 2 mins longer, or until cheese melts. Garnish with lettuce, tomatoes, olives and sour cream if desired.