Preheat oven to 350°F.
Add the orange juice, lime juice, garlic, cilantro, lime zest, cumin, oregano, salt, and black ground pepper to a food processor.
Process for 10 seconds. You don’t want the sauce to become too creamy.
Add the olive oil and process for 5 seconds, just to combine slightly.
Add the chicken and chopped onion to a large bowl.
Pour half of the mojo sauce over the chicken and onions. Cover with cling film, and marinate in the fridge for 3 hours.
Set aside the remaining half of the mojo sauce for later use.
When the chicken is done marinating, add chicken and onions to the baking tray, together with the sauce it marinated in.
Bake at 350°F for 35-40 minutes, or until cooked through to 165°F internally.