Preheat your oven to 375°F (190°C).
In a mixing bowl, combine soy sauce, brown sugar, olive oil, minced garlic, grated ginger, black pepper, salt, and paprika. Mix well to create a marinade.
Place the pork loin in a roasting pan. Pour the marinade over the pork, ensuring it is well coated. Allow it to marinate for at least 10 minutes, or longer in the fridge if time permits.
Scatter the diced pineapple around the pork loin in the roasting pan.
Bake in the preheated oven for about 45 minutes or until the internal temperature of the pork reaches 145°F (63°C). Use a meat thermometer to check the temperature.
Once cooked, remove the pork from the oven and cover it with aluminum foil. Let it rest for 10 minutes before slicing.
If you want a thicker sauce, in a small saucepan over medium heat, combine the remaining marinade with ¼ cup of water. If desired, mix in the cornstarch to thicken. Cook until bubbly and thickened.
Slice the pork loin and serve with the pineapple and drizzled sauce.