1Heat oven to 400ºF. Grease bottom and side of glass pie plate, 9x1 1/4 inches. Mix chicken, onion and seasoning mix. Sprinkle in pie plate.
2Stir together Bisquick, milk and eggs with fork until blended. Pour into pie plate.
3Bake 30 to 35 mintues or until knife inserted in center comes out clean. Sprinkle with cheese. Bake 1 to 2 minutes longer or until cheese is melted. Garnish with lettuce, tomatoes and sour cream if desired.