Pat the chicken breasts dry and season on both sides with salt and pepper.
In a large skillet, heat the olive oil over medium heat. Add the chicken breasts and cook for about 4-5 minutes per side, or until they are browned and almost cooked through. Remove the chicken from the skillet and set aside.
In the same skillet, add the chopped onion and cook for about 3-4 minutes, or until softened. Add the minced garlic and cook for an additional 1 minute.
Stir in the uncooked rice, diced tomatoes with their juice, chicken broth, Kalamata olives, roasted red peppers, oregano, paprika, and crushed red pepper flakes (if using). Mix well.
Place the partially cooked chicken breasts on top of the rice mixture in the skillet. Reduce the heat to low, cover, and cook for about 20-25 minutes, or until the rice is cooked through and the chicken is no longer pink in the center.
Remove the skillet from heat. Sprinkle the crumbled feta cheese, chopped fresh parsley, and lemon slices on top of the chicken and rice.
Serve immediately.