Preheat oven to 425°F (220°C). Bring a large pot of salted water to boil and par-cook rigatoni for 6 min. Drain well, reserving 1/2 cup (125 mL) of cooking water. Transfer pasta to an oiled 11 x 9-in. (2.5 L) baking dish. Set aside.
Meanwhile, in a bowl or large measuring cup, combine marinara sauce, pasta water, half of the basil leaves, torn into pieces, and chopped parsley. Season with salt and pepper and pour evenly over the dish. Squeeze sausages out of their casings, thinly slice and scatter on top of the pasta. Sprinkle with bread crumbs and arrange bocconcini slices on top.
Bake for 15 min., until sausage is cooked through and cheese is golden and bubbling. Let cool slightly, garnish with the remaining basil leaves, and serve.