Deep-dish Taco Squares

Here's another recipe from one of my new cookbooks. I LOVED this recipe and so did most of my family. Only one of my kids wasn't a fan but I think that was because of the sour cream, she's not really a sour cream fan. Anyway this was super easy to put together and REALLY yummy.
1/2 lb. lean ground beef
1/4 c. chopped onion
2 T. taco seasoning mix
1 c. bisquick mix
1/4 c. cold water
1/2 c. sour cream
1/3 c. mayonnaise
1/2 c. shredded cheddar cheese
1 med. tomato, chopped
1 (4.5 oz.) can chopped green chiles

Preheat oven to 375F. Spray 8-inch square baking dish with cooking spray. Over med-high heat cook ground beef and onions until thoroughly cooked. Drain and then stir taco seasoning into beef mixture until blended. In a med. bowl stir bisquick and water together until it forms a soft dough. Put dough mixture into the square dish and pat down so it's evenly spread and about 1/2 inch up the sides. In a med. bowl mix sour cream, mayonnaise and cheese until blended. Layer beef mixture, tomato and chiles over dough. Spoon sour cream mixture over the top. Bake for 25-30 minutes or until edges of dough are light golden brown.