Place the chicken thighs in a large zip-top bag or a bowl.
Add the avocado oil, lemon zest, lemon juice, minced garlic, minced rosemary, onion powder, and sea salt to the bag.
Seal the bag and shake or massage it until the chicken is evenly coated with the marinade.
Marinate in the refrigerator for at least 1 hour or up to 8 hours.
When ready to cook, preheat the oven to 375°F (190°C) and transfer the chicken to a large casserole or baking dish, skin-side up, spacing pieces slightly apart.
Bake at 375°F for 35 minutes.
Increase the oven temperature to 425°F (220°C) and bake an additional 20 to 30 minutes, or until the skin is as crisp as you like and the internal temperature reaches 165°F (74°C).
Remove from the oven and let rest a few minutes before serving.