Begin by zesting and juicing the selected citrus fruits—lemons, limes, and oranges—in a mixing bowl. Add freshly minced garlic and finely chopped shallots, followed by olive oil, brown sugar, salt, pepper, chopped rosemary, parsley, and red pepper flakes. Whisk the mixture until fully combined.

Lightly pound or butterfly the chicken for even thickness, then place it in a resealable bag or shallow dish. Pour half of the citrus marinade over the chicken, seal or cover it, and let it marinate in the refrigerator for at least 30 minutes.

Preheat your grill to medium-high heat (about 400°F). Brush the grill grates with a light coating of oil to prevent sticking.

Remove the chicken from the marinade, letting any excess drip off. Place the chicken on the hot grill and cook for 6–7 minutes per side until it reaches an internal temperature of 165°F.

After cooking, transfer the chicken to a cutting board and let it rest for about 5 minutes. Slice and garnish with freshly chopped parsley before serving.