Preheat oven to 325°F (165°C) and pat turkey dry with paper towels.
Season turkey inside and out with salt and pepper.
Mix butter, olive oil, lemon juice, zest, garlic, parsley, salt, and pepper.
Gently loosen the turkey skin and spread the flavored butter under and over the skin.
Stuff the cavity with onion, garlic, parsley, and lemon.
Place turkey breast-side up in a roasting pan and drizzle with olive oil.
Roast for about 15 minutes per pound, basting occasionally. Cover loosely with foil if browning too fast.
Turkey is done when internal temp reaches 165°F (74°C). Let it rest 20–30 minutes before carving.