Preheat your Blackstone griddle to medium-high heat.
In a large bowl, combine olive oil, garlic powder, onion powder, smoked paprika, salt, and black pepper. Mix well.
Add the chicken thighs to the bowl and toss until they are evenly coated with the marinade. Let them marinate for at least 15 minutes for better flavor.
Place the marinated chicken thighs on the preheated griddle. Cook for about 5-7 minutes on each side, or until the internal temperature reaches 165°F.
During the last minute of cooking, sprinkle the grated Parmesan cheese over the chicken and allow it to melt.
Remove the chicken from the griddle and drizzle with lemon juice. Garnish with chopped parsley before serving.