Preheat the oven to 350°F (180°C). Peel and finely slice the onions. Heat the olive oil in a saucepan over high heat. When the oil is hot, add the sliced onions and cook for about 3 minutes, or until they are translucent. Add the ground beef and cook for about 10 minutes, stirring well. Season with salt and pepper to taste.

Once the ground beef is cooked, add the tomato sauce and paprika to the saucepan. Reduce the heat to low and cook for a few more minutes, stirring frequently. Remove the saucepan from the heat and set aside.

Grease a baking dish with butter. Fill the cannelloni noodles with the meat mixture using a small spoon, then arrange them side by side in the bottom of the dish. Pour the tomato sauce over the cannelloni, then sprinkle with grated Parmesan cheese.

Bake the dish in the preheated oven for about 25 minutes, or until the cheese on top is golden brown. Serve these Sicilian-style cannelloni hot, accompanied by a green salad.