HEAT oven to 450ºF. Cover baking sheet with heavy duty aluminum foil.
SEASON chicken with 1/4 teaspoon of the salt and pepper. Heat oil in large skillet on medium-high heat. Add chicken. Sauté 2 minutes, or until exterior is no longer pink. Remove chicken from pan with slotted spoon.
ADD onion and mushrooms to pan; season with remaining 1/4 teaspoon salt. Sauté 3 minutes, or until onion is translucent. Remove pan from heat.
STIR barbeque sauce into chicken and vegetables. Place pizza crusts on baking sheets. Arrange half of cheese on crusts. Top both with chicken mixture. Top chicken with remaining cheese.
BAKE 10 to 12 minutes, or until crust is crisp and cheese is melted. Let stand 3 minutes before cutting. Serve immediately.
Serving Size (1 slice, 1/4 12" pizza), Calories 440 (Calories from Fat 190), Total Fat 21g (Saturated Fat 9g, Trans Fat 0g), Cholesterol 65mg, Sodium 1040mg, Total Carbohydrate 37g (Dietary Fiber 2g, Sugars 7g), Protein 24g; Percent Daily Value*: Vitamin A 6%, Vitamin C 2%, Calcium 40%, Iron 15%.
*Percent Daily Values are based on a 2,000 calorie diet.