Slice the chicken sausage into 1/2-inch thick rounds. Chop the onion and mince the garlic. Cut the broccoli into bite-sized florets.

Heat olive oil in a large pot or Dutch oven over medium-high heat. Add the sliced chicken sausage and cook for 3-5 minutes, turning occasionally, until lightly browned and heated through. Remove the sausage from the pot and set aside, leaving any rendered fat in the pot.

Add the chopped onion to the pot and cook for 4-6 minutes, or until softened and translucent, scraping up any browned bits from the bottom of the pot. Add the minced garlic, Italian seasoning, and red pepper flakes (if using), and cook for another minute until fragrant.

Pour in the low-sodium chicken broth and bring it to a gentle boil. Stir in the orzo pasta. Reduce the heat to medium-low, cover, and simmer for 8-10 minutes, or until the orzo is almost al dente, stirring occasionally to prevent sticking.

Stir in the broccoli florets and the cooked chicken sausage. Continue to simmer, uncovered, for another 3-5 minutes, or until the broccoli is tender-crisp and the orzo is fully cooked.

Taste the soup and season with salt and black pepper as needed. Stir in fresh lemon juice, if desired, for an extra burst of flavor. Ladle the hot soup into bowls. Garnish with fresh chopped parsley and grated Parmesan cheese, if using.