Add all chicken marinade ingredients (except for chicken thighs) to a medium bowl and whisk until combined. Then place chicken thighs in a large ziplock bag and pour in marinade, massage bag to combine everything. Marinate in fridge for at least 30 minutes or overnight.
Preheat oven to 350 F. Remove chicken from fridge to come to room temp while preheating oven.
In a large ovenproof skillet, heat 2 tbsp olive oil over medium-high heat. Transfer chicken thighs to skillet, skin side down, and cook for 5 minutes per side until golden brown. Remove from skillet and set aside. Discard excess fat and brown bits from skillet.
Turn heat down to medium-low and add the diced onion and minced garlic to the skillet. Cook for 4 minutes, stirring often, until translucent and soft. Add 1 cup washed long grain rice and stir to cook for a couple of minutes. Then add 2 cups chicken broth, juice from 1 lemon, dried oregano, salt and pepper.
Bring rice to a light boil and let simmer for 30 seconds. Transfer chicken thighs to the skillet and arrange on top of the rice with some room in-between each. Cover the skillet with a lid and transfer to preheated oven to bake for 30 minutes.
After 30 minutes, remove the lid and continue to bake in the oven for 10 more minutes or until chicken is cooked through (internal temp 165 F). If desired, broil for 2-3 minutes longer for extra color and crispiness.
Remove from oven and let rest for 5 minutes. Fluff rice with fork before serving. Garnish with fresh parsley and extra lemon slices.