In a large skillet, cook and stir the ground beef and onion until beef is brown. Drain.
Add drained beef mixture back to skillet and mix in taco seasoning.
Spread mixture in a 9-inch pie plate.
Sprinkle with chilies.
In a medium bowl, beat milk, baking mix, and eggs until smooth.
Pour milk mixture over beef.
Bake uncovered in a 400º oven for 30-35 minutes.
Top with sliced tomatoes, sprinkle with cheese, and return to oven.
Bake an additional 8 – 10 minutes, or until golden brown.
Top with sour cream, chopped tomato, and shredded lettuce.
Serve immediately.