Preheat oven to 350 degrees f.
Heat oil in a large OVEN SAFE skillet over medium-high heat.
Add chicken, season with sea salt and pepper, then sear until golden, 2 minutes per side. Transfer to a plate.
Reduce heat to medium-low and add garlic to skillet.
Cook until fragrant, for about 1 minute. Add crushed tomatoes, crushed red pepper flakes, and basil. Simmer for about 5 minutes.
Return chicken to skillet and arrange it nicely among the sauce.
Top chicken with mozzarella and pepperoni, then place entire skillet in your preheated oven, and bake until cooked through and no longer pink in the inside, about 15 minutes.
Garnish with fresh chopped basil and enjoy!