Heat a large non-stick skillet to medium high heat. Spray with olive oil or cooking spray. Sprinkle each side of chicken tenderloins with salt and pepper and add to the pan. Cook on each side about 3-4 minutes or until cooked. Remove chicken from pan and cover to keep warm.
Add sliced mushrooms to the skillet and sautéed about 2 minutes. Remove from pan and add to chicken, covering to keep warm. Add onion and garlic to the skillet. Sauté about 2 minutes. Add 2 tbsp sun-dried tomato pesto, stirring to coat. Add seasonings and diced tomatoes. Turn heat down to low and let cook about 3-4 minutes.
Add chicken and mushrooms back to skillet, stirring ingredients together careful to not spill and allowing to heat another 2 minutes. Remove from skillet to serving dish and serve.