In a large soup pot, sauté the sausage over medium-high heat for 7-10 minutes, breaking it apart as it cooks, until browned. Remove from the pot and set aside on a paper towel-lined plate, leaving about 1 tablespoon of fat in the pot.,Add the diced onion and celery to the pot, cooking for 4-5 minutes until softened. Add the flour and garlic, and cook for another minute, stirring constantly.,Slowly pour in the chicken broth, stirring to dissolve the flour. Add the diced tomatoes, oregano, and browned sausage back into the pot. Bring the soup to a gentle boil over high heat.,Once boiling, add the heavy cream and orzo. Reduce the heat and simmer for about 12 minutes, or until the orzo is tender, stirring occasionally.,Stir in the spinach until wilted. Season with salt and pepper to taste, and serve warm.