To make the filling: Heat the oil and the butter in a pan over medium heat, add the bell pepper, onion, scallions and garlic, stirring often. When the vegetables are soft add the ground beef and pork. Stir well and cook for 15 minutes over medium-low heat. Season with salt and pepper and continue cooking for 5 minutes more. Add the potatoes, mix well and reserve.
Wash the pepinos and cook them in salted water for about 5 to 10 minutes until soft. Make a slice in the middle of each pepino and take out the black seeds and veins. Fill them with the meat and potato mixture and place on a plate.
To make the sauce: in a saucepan heat the oil and butter, add the garlic and onion and sauté until tender. Add the tomatoes and cook until very soft. Add the beef broth, salt, and pepper. Place the filled pepinos in one layer, cover the pan and cook over medium-low heat for 25 minutes. Add the heavy cream and cook for about 5 minutes more. Serve them immediately with white rice and sauce on top.