Coat a small nonstick skillet with cooking spray; place over medium heat until hot. Add onion, green pepper, 1/8 teaspoon garlic powder, and pepper; saute until onion is tender. Remove from heat; stir in chicken and tomato. Set aside.
Combine baking mix, remaining 1/8 teaspoon garlic powder, and milk in a small bowl, stirring well. Sprinkle 1/2 teaspoon flour evenly over work surface. Turn dough out onto floured surface, and knead 4 or 5 times.
Divide dough in half; roll each portion into a 4-inch circle. Spoon chicken mixture evenly over half of each circle; sprinkle cheese evenly over each. Brush edges of circles with water; fold circles in half, and seal. Coat with cooking spray; place on a baking sheet coated with cooking spray. Bake at 350° for 10 to 12 minutes or until golden. Serve immediately.