Impossibly Easy Chicken Taco Pie

2 cups cut up cooked chicken

1/2 cup chopped onion

2 Tbsp taco seasoning mix

1 cup bisquick mix

1 cup milk

2 eggs

1 cup shredded cheddar cheese

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