Heat the oven to 350 degrees. In a large skillet, warm the oil over medium heat. Stir in the onion and cook for 3 minutes. Add the ground beef and brown thoroughly, breaking it up with a wooden spoon. Spoon away any excess fat, then stir in the flour, beans, and spices and cook the filling for 2 minutes more.
Line a 9-inch pie plate with the crust. Add the filling and sprinkle on the cheese.
Bake the pie on the center rack until the filling is bubbly and the crust golden brown, about 40 minutes. Let cool for 15 minutes, then top with lettuce, tomato, avocado, and if you like, more cheese. Serve right away.