Boil the potatoes in salted water until fork-tender, about 12–15 minutes. Drain very well.
In a skillet over medium heat, sauté the onion in 1 tbsp oil (assumption) until softened. Add ground beef and cook until browned.
Season the beef with 1 1/2 tsp salt, 1 1/2 tsp black pepper, paprika, and garlic powder. Stir in tomato sauce and simmer 2–3 minutes until thick and saucy.
Mash drained potatoes with butter and chopped parsley until fluffy.
Divide the mash into 6 portions (assumption). Shape into balls and place in a baking dish. Press a deep well in each.
Spoon beef filling into each well, then top with grated cheese.
Bake at 400°F (200°C) (assumption) for 10–15 minutes (assumption) until cheese is melted and centers are hot. Rest 2–3 minutes, then serve warm.