lemon chicken orzo soup

Ingredients:

1 tablespoon olive oil
1 onion, diced
2 carrots, diced
2 celery stalks, diced
2 cloves garlic, minced
6 cups chicken broth
1 cup cooked shredded chicken (rotisserie chicken works well)
1/2 cup uncooked orzo pasta
Zest and juice of 1 lemon
Salt and pepper to taste
Fresh parsley, chopped, for garnish