Preheat oven to 400?F

Bring med. pot of salted water to a boil

Add pasta and cook until tender, stirring occasionally (about 5 min.)

Drain pasta and place in a greased 8x8 baking dish

Meanwhile, heat olive oil in a med. saute pan over med. heat

Add chicken and cook for 3 minutes

Stir in onion and garlic, cook until onions are soft and chicken is cooked through, about 5 minutes

Add chicken to the baking dish with pasta

Stir in canned tomatoes, mozzarella, parsley, salt, and pepper

In a small bowl, mix bread crumbs and Parmesan, then sprinkle over the pasta mixture

Dot the top with small bits of butter

Bake until the top is golden brown, about 30 minutes