Preheat your oven to 425°F (220°C). Line a baking sheet with aluminum foil and place a wire rack on top.
In a large bowl, combine the olive oil, smoked paprika, garlic powder, onion powder, salt, black pepper, and cayenne pepper (if using). Mix well to create a marinade.
Add the chicken thighs to the bowl and toss until they are evenly coated with the marinade. Let the chicken marinate for at least 30 minutes at room temperature, or refrigerate for up to 4 hours.
Arrange the marinated chicken thighs skin-side up on the wire rack.
Bake in the preheated oven for 35-40 minutes, or until the chicken reaches an internal temperature of 165°F (75°C) and the skin is crispy and golden brown.
Remove from the oven and let the chicken rest for 5 minutes before serving. Garnish with chopped parsley if desired.