Grease a 9-inch pie plate.
In a heavy skillet, cook ground beef with onion over medium heat, stirring occasionally. Drain. Stir in taco seasoning; spread in pie plate. Top with green chiles and about half of the chopped tomatoes.
In a mixing bowl, combine Bisquick, milk, and eggs; stir until well blended. Pour over the mixture in the pie plate.
Bake at 400° for about 25 minutes, or until a knife inserted in center comes out clean. Sprinkle with the shredded cheese. Bake for a few more minutes, until cheese is melted. Serve with salsa, sour cream, and chopped green onions, if desired.