1. Preheat oven to 400F (200C).
2. Place ground beef, onion, riced cauliflower, paprika, Italian seasoning, salt and pepper into a food processor. Process until everything is thoroughly minced. Add egg, and pulse several more times.
3. Wet your hands and form the mixture into 13 lightly flattened meatballs (use a tablespoon or an ice cream scoop).
4. Slice potatoes. Spread about 1 cup of marinara sauce in the bottom of a baking dish.
5. Arrange cherry tomatoes along the sides of the baking dish, then arrange meatballs and potatoes in the middle, alternating them.
6. Top with the rest of the marinara sauce. Lightly sprinkle with salt, with a bit extra on the potatoes, and drizzle with oil.
7. Cover with foil and bake in the preheated oven for 40 minutes, remove the foil and bake for another 15 minutes, until the potatoes are cooked through.
8. Sprinkle with parsley and serve.