Heat the olive oil in a 4.5-quart pot over medium-high heat until shimmering, about 2 minutes.

Add the Italian sausage to the pot, breaking it apart and cooking until browned and crispy, about 5–7 minutes. Transfer to a plate and set aside.

Drain excess grease, leaving about a teaspoon, then sauté the chopped onion and diced celery for 3–4 minutes. Add minced garlic in the last minute.

Return the browned sausage to the pot, along with orzo pasta, diced tomatoes with juice, and chicken broth. Sprinkle in Italian seasoning, sea salt, and black pepper to taste.

Increase heat to high and bring the soup to a rolling boil, about 5 minutes, then reduce temperature to low.

Let the soup simmer for 10-15 minutes, stirring occasionally until the orzo is al dente.

Adjust consistency with water or broth as needed.

Ladle the soup into bowls, garnishing with fresh parsley and grated Parmesan if desired.