Preheat the oven to 375°F (190°C).
Pat the 28 ounces boneless, skinless chicken breasts dry with paper towels. Season both sides with kosher salt and freshly ground black pepper to taste.
Heat 2 tablespoons olive oil in a large skillet over medium-high heat until shimmering.
Sear the chicken in the hot skillet for about 2–3 minutes per side, until golden brown. Transfer the seared chicken to a single layer in an oven-safe baking dish.
In a bowl, mix 1 cup ricotta cheese, 3 minced garlic cloves, 1 teaspoon Italian seasoning, and 1/2 teaspoon dried oregano until evenly combined.
Spread the ricotta mixture evenly over each piece of chicken in the baking dish.
Pour 24 ounces marinara sauce evenly over and around the ricotta-topped chicken.
Bake uncovered at 375°F for 15–20 minutes, or until the thickest part of the chicken reaches an internal temperature of 165°F when checked with an instant-read thermometer.
Remove the dish from the oven, sprinkle 1 cup shredded mozzarella cheese evenly over the chicken, and return to the oven for an additional 5 minutes, or until the mozzarella is melted.
Remove from the oven, garnish with fresh basil leaves if desired, and let sit a couple of minutes before serving.