- With the rack in the middle position, preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
- On a work surface, slice the rolls open lengthwise without going all the way through to the other side and open like a book. Place on the prepared sheet and top the inside of the bread with the cheese. Set aside.
- In a non-stick skillet over high heat, soften the onion in the oil. Add the sausage meat and brown, breaking it up with a wooden spoon into pieces the size of small meatballs. Add the tomatoes. Bring to a boil and cook over medium heat until the liquid has completely evaporated, about 10 minutes. Season with salt and pepper.
- Meanwhile, in a pot of salted boiling water, blanch the rapini for 2 to 3 minutes or until al dente. Drain and lightly drizzle with oil.
- Heat the rolls in the oven for 3 to 4 minutes. Fill with the sausage mixture and rapini. Serve immediately.