Preheat your oven to 375°F (190°C).
In a medium bowl, combine the ricotta cheese, chopped spinach, mozzarella cheese, Parmesan cheese, minced garlic, oregano, basil, salt, black pepper, and red pepper flakes (if using). Mix well until all ingredients are evenly incorporated.
Pat the chicken breasts dry with paper towels and place them in a baking dish. Drizzle olive oil over the chicken and rub it in to coat evenly.
Spoon the ricotta mixture generously over the top of each chicken breast, spreading it out evenly.
Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (75°C).
For a golden top, switch the oven to broil for the last 2-3 minutes of cooking, keeping a close eye to prevent burning.
Remove from the oven and let the chicken rest for 5 minutes before serving. Garnish with fresh basil leaves if desired.