1Heat oven to 375°F. Spray 13x9-inch pan with cooking spray. In 10-inch skillet, cook beef and chili powder over medium-high heat 6 to 8 minutes, stirring occasionally, until thoroughly cooked; drain. Set aside.
2In small bowl, mix sour cream, mayonnaise, cheese and onion; set aside.
3In medium bowl, stir Bisquick mix and cold water with fork until soft dough forms. Using fingers dipped in Bisquick mix, press dough in bottom and 1/2 inch up sides of pan. Layer beef, tomatoes and bell pepper on dough. Spoon sour cream mixture over top; spread evenly over vegetables to cover.
4Bake uncovered 25 to 30 minutes or until edges of dough are light brown.