The night before, prepare the turkey by removing the giblets and neck from the cavity. Rinse off, pat dry, and set on a roasting rack, breast side up. Gently slide your hand in between the skin and breast, wiggling your fingers as you move through to create a pocket.
In a mixing bowl combine yogurt, rub, 2 Tbsp olive oil, minced garlic, sea salt, and black pepper.
Spoon ½ of the yogurt mixture under the skin and massage around, rubbing it into all areas you can reach. Rub the remaining yogurt mixture around the outside of the bird on both sides.
Arrange sliced lemons under the skin and the fill the center cavity with the onions. Drizzle everything with remaining 2 Tbsp olive oil.
Wrap the bird in plastic wrap and refrigerate until ready to cook (at least 6 hours.)
The day of cooking: Remove the marinated bird from the refrigerator at least 1 hour prior to cooking to bring up to room temperature. Remove the plastic wrap. Pour the chicken stock in the bottom of the roasting pan.
Preheat the oven to 450°F.
Bake for 30 minutes then reduce the heat to 350°F.
Continue roasting until the internal temperature reaches 165°, about 2 to 2.5 hours. Cover with foil if the meat starts getting too dark. Let rest at least 20 minutes before carving.