In a large skillet over medium heat, add oil. When hot, add onions and sauté for 2 minutes. Add red peppers and cook for a couple of minutes. Add ground beef and season with salt and pepper. Cook until no longer pink, breaking the meat into small pieces. Just before the meat is done, add garlic and sauté for 1 minute. Add oregano and stir for 1 minute. Adjust seasoning if needed.
Drain meat mixture into a colander for a few minutes to remove excess fat. Transfer meat mixture to a large 9×13 baking dish and spread it out evenly. Add corn and level it out as well. Top with mashed potatoes, spread out evenly, leaving a small gap between potatoes and baking dish to help from boiling over. Add butter and spread it over the potatoes before sprinkling on paprika and parsley.
Transfer to a 350ºF preheated oven and bake for 1 hour or until it bubbles and the top gets golden brown. Remove from heat and let it cool for 15 minutes before serving. Serves 8 to 10.