White Bean Chicken (or Turkey) Chili

1 tablespoon olive oil
1/2 cup diced onion
2 (14.5 ounce) cans Great Northern Beans, undrained
2 cups cooked, diced chicken (or turkey)
2 cups chicken broth
3/4 cup salsa (I use Pace Chunky Medium)
1 teaspoon dried oregano
1/2 teaspoon celery salt
1 1/2 cups shredded mozzarella cheese

In a medium saucepan, heat the olive oil over medium heat. Add onions and cook until onions are translucent, about 5 minutes. Add the remainder of the ingredients, except the mozzarella cheese. Heat over medium heat, stirring occasionally, until the soup comes to a simmer. Add the mozzarella cheese one handful at a time, stirring to let each addition melt before adding the next. Stir to combine and make sure all the cheese has melted and serve.