Place the chicken breasts between sheets of plastic wrap and pound the thickest part until about ¾ inch thick. If using large breasts, cut them into evenly sized portions.
In a small bowl, combine the herbs, lemon zest, garlic, salt, pepper, chili flakes, and olive oil to make the Chicken Marinade.
Reserve 2 tablespoons of the marinade for serving.
Place the chicken into a bowl, baking dish, or zip-top bag. Pour the remaining marinade over the chicken and coat well.
Marinate for at least 30 minutes, or refrigerate for several hours or overnight for even more flavor.
Preheat the grill to medium-high heat.
Remove the chicken, allowing excess oil to drip off before placing it on the grill.
Cut the zested lemon in half and place the cut side down on the grill. Add tomatoes or other vegetables if desired.
Grill the Grilled Lemon Chicken for 5–6 minutes on the first side until distinct grill marks appear.
Flip and cook another 5–7 minutes until the internal temperature reaches 160°F (71°C). Move to indirect heat if needed to finish cooking without burning.
Allow the chicken to rest for 5–10 minutes before serving.
Arrange on a serving platter, squeeze the grilled lemon over the chicken, drizzle with the reserved marinade, garnish with fresh herbs, and enjoy.