Steak and Veggie Sandwiches

1 pound beef round tip steak, cut 1/8 to 1/4 inch thick
2 teaspoons olive oil
1 medium zucchini, cut into 1/4-inch-thick slices
1 medium onion, thinly sliced
1 medium red bell pepper, cut into thin strips
1 teaspoon Italian seasoning, crushed
1 teaspoon olive oil
1/4 teaspoon salt
1/4 teaspoon pepper
4 crusty hoagie rolls, about 6 inches long, split
4 (3/4 ounce) slices mozzarella cheese
Cut beef into strips. Set aside.