Combine baby back ribs, onion, olive oil, lemon juice, oregano, honey, garlic, salt, and pepper in a large resealable plastic bag. Turn to ensure ribs are well coated.

Marinate in the refrigerator, turning occasionally, 4 to 8 hours.

Preheat oven to 400 degrees F (200 degrees C). Line a baking sheet with aluminum foil; grease with cooking spray.

Arrange ribs on the prepared baking sheet, leaving space between them.

Bake in the preheated oven until browned, about 10 minutes. Reduce oven temperature to 300 degrees F (150 degrees C). Continue baking until ribs are tender, about 1 hour.