Prep Chicken: Place each chicken breast between two sheets of plastic wrap or parchment paper. Pound with a meat mallet or rolling pin until about 1/4 inch thick.
Marinate: In a large bowl, mix lemon juice, olive oil, garlic, oregano, thyme, salt, and pepper. Add the chicken, ensuring it's well-coated. Marinate for at least 30 minutes.
Grill: Preheat the grill to medium-high heat. Grill the chicken for 3-4 minutes per side or until fully cooked and has nice grill marks.
Serve: Remove from the grill and let rest for a few minutes. Serve with a fresh salad or your favorite side dish.