Pound the chicken breasts to even ¾-inch thickness between plastic wrap using a meat mallet or rolling pin.
Whisk together the olive oil, lemon juice, minced garlic, honey, Dijon mustard, oregano, smoked paprika, salt, black pepper, and red pepper flakes until well combined.
Place the pounded chicken in a large zip-top bag or shallow dish. Pour the marinade over, turning to coat. Seal and refrigerate for 20 minutes and up to 4 hours.
Preheat the grill to medium-high heat, about 400–450°F (200–230°C). Clean the grates well with a grill brush, then brush them with oil using a folded paper towel held with tongs.
Remove the chicken from the marinade, letting the excess drip off (discard the used marinade). Place on the hot side of the grill. Cook undisturbed for 5–6 minutes, flip once, and cook another 5–6 minutes until the internal temperature reaches 165°F (74°C).
Transfer the grilled chicken to a clean plate and let it rest for 5 minutes. Slice against the grain, squeeze fresh lemon over the top, shower with chopped herbs, and serve.