Whisk together the olive oil, soy sauce, garlic, mustard, salt, and pepper in a bowl.
Place the pork loin in a large resealable plastic bag and pour in the marinade. Marinate in the refrigerator at least 1 hour before cooking.
Preheat oven to 350°F.
Transfer the pork loin to a baking dish; pour marinade over the pork.
Cook in the preheated oven until the pork is no longer pink in the center, 45 to 60 minutes. An instant-read thermometer inserted into the center should read 145°F.