In a blender or food processor, combine the ricotta with the oregano, salt, and pepper. Process to blend.
Rub the chicken with the garlic powder. Heat the oil in a large skillet over medium-high heat. Add the chicken and cook for 12 minute per side. Place the chicken breast, side by side, in a large baking dish and allow to cool.
Preheat the oven to 350 degrees.
Spoon 1/4 cup of the cheese mixture and 1/4 cup tomoatoe onto each chicken breast. Top each chicken breast with 1 slice mozzarella. Bake for 20 min/, or until a thermometer inserted in the thickest portion of a breast registers 170 degrees and the juices run clear.