Prep the ingredients: dice 1 medium onion; chop 2 medium carrots and 3 stalks celery; mince 2 cloves garlic; dice 1 pound chicken breast; chop 1/4 cup fresh parsley; have 1 medium lemon ready.
Heat 1 tablespoon olive oil in a large pot over medium-high heat.
Add the diced onion, chopped carrots, chopped celery, and minced garlic to the pot. Cook, stirring occasionally, until the onion is softened, approximately 10 minutes.
Add the diced chicken to the pot and season with 1/2 teaspoon ground black pepper and 1/2 teaspoon salt. Cook, stirring frequently, until the chicken is mostly opaque on the outside.
Add 6 cups low-sodium chicken broth, 1 cup dry orzo, 1/2 teaspoon Worcestershire sauce, 1 bay leaf, 1 tablespoon fresh thyme, and 1 teaspoon fresh rosemary to the pot. Bring the mixture to a boil.
Reduce heat to medium-low, cover, and simmer until the orzo is tender but still slightly firm, about 6 to 8 minutes.
Stir in 1 cup frozen green peas and allow them to heat through.
Remove the pot from heat, discard the bay leaf, and squeeze the juice of the 1 medium lemon into the soup.
Portion the soup into bowls and garnish each serving with the 1/4 cup chopped fresh parsley. Serve.