In a bowl, stir together the muffin mix, flour and chili powder. Beat in the egg and milk. Pat into the prepared pan with floured hands.
Spread the refried beans, then the chili, over the crust. Sprinkle with cheese. Add optional toppings if desired.
Bake for 15 to 20 minutes, until cheese is melted and crust is firm. Remove from oven and let stand 5 minutes before cutting into squares.
Makes 12 servings.