Italian Baked Chicken and Pastina

Preheat the oven to 400 degrees F. Bring a medium pot of salted water to a boil over high heat. Add the pasta and cook until just tender, stirring occasionally, about 5 minutes. Drain pasta into a large mixing bowl. Meanwhile, put the olive oil in a medium saute pan over medium heat. Add the chicken and cook for 3 minutes. Add the onions and garlic, stirring to combine, and cook until the onions are soft and the chicken is cooked through, about 5 minutes more. Put the chicken mixture into the bowl with the cooked pasta. Add the canned tomatoes, mozzarella cheese, parsley, salt, and pepper. Stir to combine. Place the mixture in a buttered 8 by 8 by 2-inch baking dish . In a small bowl mix together the bread crumbs and the Parmesan cheese . Sprinkle over the top of the pasta mixture. Dot the top with small bits of butter. Bake until the top is golden brown, about 30 minutes.