Preheat oven to 350 degrees Fahrenheit.

Fry onion in a non-stick pan over medium heat. Add diced mushrooms and fry until mushrooms are dark. Sprinkle with salt and pepper. Set aside to cool.

Flatten chicken breasts. Spoon two tablespoons of mushroom mixture onto each chicken breast. Roll tightly and fasten with toothpicks. Place each one seam side down in a lightly greased dish. Brush some olive oil over schnitzels.

Bake covered for 30–40 minutes or until chicken is cooked through and is no longer pink. Remove toothpicks and serve.