Sausage, Peppers, and Onions Stuffed Shells

package frozen stuffed shells (8 shells)

tbsps olive oil

Italian sausage (3 links should be close to 8 oz)

red bell pepper, diced

green bell pepper, diced

onion, diced

dried oregano

jar (1 lb 8 oz)  Ragú® Old World Style® Traditional Sauce

mozzarella cheese, shredded