Step 1: Prepare the chicken: Place each chicken breast between two sheets of plastic wrap. Using a meat mallet or a heavy-bottomed pan, pound the chicken to an even thickness of about 3/4 inch. This ensures even cooking.
Step 2: Make the marinade: In a medium bowl, whisk together the fresh lemon juice, lemon zest, olive oil, minced garlic, chopped fresh rosemary, chopped fresh thyme, sea salt, and black pepper.
Step 3: Marinate the chicken: Place the pounded chicken breasts in a non-reactive dish or a large resealable bag. Pour the marinade over the chicken, ensuring all pieces are well coated. Cover and refrigerate for at least 30 minutes, or preferably 2-4 hours. For maximum flavor, you can marinate overnight.
Step 4: Preheat the grill: Preheat your outdoor grill to medium-high heat (about 400-450°F or 200-230°C). Clean the grill grates thoroughly with a wire brush, then lightly oil them to prevent sticking.
Step 5: Grill the chicken: Remove chicken from the marinade (discarding any remaining marinade). Place the chicken breasts on the hot, oiled grill grates. Grill for 5-7 minutes per side, or until the internal temperature reaches 165°F (74°C) at its thickest part. For crosshatch grill marks, rotate the chicken 45 degrees after 2-3 minutes on the first side before flipping.
Step 6: Rest and serve: Transfer the grilled chicken to a clean cutting board or platter. Tent loosely with foil and let it rest for 5-10 minutes before slicing and serving. This allows the juices to redistribute, resulting in more tender and juicy chicken.