Season the chicken breasts with salt and black pepper on both sides.
In a large skillet, heat the olive oil over medium-high heat.
Add the chicken breasts and cook for about 6-7 minutes on each side, or until golden brown and cooked through. Remove the chicken from the skillet and set aside.
In the same skillet, add the diced onion and sauté for about 3-4 minutes until softened.
Add the minced garlic and cook for an additional minute until fragrant.
Stir in the cherry tomatoes, Kalamata olives, capers, oregano, and red pepper flakes. Cook for about 5 minutes until the tomatoes start to soften.
Return the chicken to the skillet and pour the lemon juice over the top.
Simmer for another 2-3 minutes to heat through and allow the flavors to meld.
Remove from heat and sprinkle with fresh basil before serving.