Preheat your grill to medium-high heat.
In a small saucepan, melt the butter over low heat. Add the minced garlic, sliced pepperoncini, oregano, salt, and black pepper. Stir well and let simmer for about 5 minutes to allow the flavors to meld. Remove from heat.
Pat the chicken thighs dry with paper towels and drizzle with olive oil. Season both sides with salt and pepper.
Place the chicken on the grill and cook for about 6-7 minutes on each side, or until the internal temperature reaches 165°F.
Once cooked, remove the chicken from the grill and let it rest for 5 minutes.
Drizzle the pepperoncini garlic butter over the grilled chicken and garnish with fresh parsley before serving.