Place a rack in the center of your oven and preheat the oven to 375 degrees Fahrenheit.
Season the chicken with the salt and pepper, sprinkling both sides.
In a large ovenproof skillet, heat 1 tablespoon olive oil over medium high. Once hot, add the chicken breasts, and let cook for 2 to 3 minutes, until the surface is golden brown. Flip and brown the other side. Remove to a plate (the chicken does not need to be cooked through).
Reduce the heat to medium. Add the remaining 1 tablespoon oil and the onion. Sauté until the onion is tender, about 5 minutes.
Add in the garlic, Italian seasoning and pasta sauce. Let simmer for 5 minutes.
Nestle the chicken back into the sauce. Sprinkle the cheese over the top of the chicken. Arrange the pepperoni slices on top.
Place the oven-safe skillet in the oven and cook for 20 to 25 minutes, or until a thermometer inserted in the thickest portion of the chicken registers 165 degrees Fahrenheit.
Remove from the oven and enjoy.