Preheat the oven to 400 °F (204 °C). Spray a 9-inch pie dish with nonstick cooking spray.
In a large skillet, cook and crumble ground beef (1 pound) and onion (1/2 cup), until the beef is done and there is no longer any pink in it. Drain excess grease. Mix in taco seasoning (1 envelope).
Layer beef on the prepared pie plate. Add green chiles (1 can) to the top of the beef in a single layer.
In a mixing bowl, whisk together Bisquick (1/2 cup), milk (1 cup), and eggs (2) until combined. Pour over beef mixture.
Bake in preheated oven until a knife inserted in the center of the pie comes out clean, about 25 minutes. Remove from oven and sprinkle with cheese (3/4 cup). Put back in the oven until cheese is melted, about 2-3 minutes. Let stand 5 minutes then top as desired and serve.