1Heat oven to 375°F. Spray 8-inch square pan or 2-quart glass baking dish with cooking spray. In small bowl, cover onion with hot water.
2In 10-inch skillet, cook beef over medium-high heat 5 to 7 minutes, stirring occasionally, until brown; drain. Stir in cheese dip. Cook 2 to 3 minutes or until hot.
3In medium bowl, mix Bisquick mix, milk and egg until blended. Pour half of the batter into pan. Top with beef mixture and bell pepper mixture. Pour remaining batter evenly over top. Drain onion; sprinkle over batter.
4Bake 40 to 45 minutes or until golden brown and center is set. Let stand 5 minutes before cutting into squares. If desired, heat leftover cheese dip as directed on jar and spoon over each serving.