Preheat your grill to medium-high heat.
In a large bowl, whisk together olive oil, lemon juice, red wine vinegar, garlic powder, dried oregano, salt, black pepper, and red pepper flakes.
Add the chicken thighs to the marinade, ensuring they are well coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
While the chicken is marinating, prepare the Salmoriglio sauce. In a small bowl, combine olive oil, lemon juice, parsley, oregano, minced garlic, salt, and pepper. Mix well and set aside.
Remove the chicken from the marinade and discard the marinade. Grill the chicken for about 6-7 minutes per side, or until the internal temperature reaches 165°F.
Once cooked, remove the chicken from the grill and let it rest for 5 minutes.
Serve the grilled chicken drizzled with Salmoriglio sauce.