In a large pot, heat 2 tablespoons of olive oil over medium heat. When the oil shimmers, add 1 pound of Italian sausage, breaking it apart with a wooden spoon. Cook until browned and crispy, about 6–8 minutes, stirring occasionally to ensure even cooking and prevent sticking.

Once the sausage is nicely browned, add 1 chopped onion to the pot. Sauté for another 4–5 minutes, stirring frequently until the onion is soft and translucent.

Stir in 3 minced garlic cloves, 1 teaspoon of dried oregano, 1 teaspoon of dried thyme, and ½ teaspoon of crushed red pepper flakes, if using. Cook for 1–2 minutes until fragrant.

Next, pour in 6 cups of chicken broth and add 1 can (14.5 ounces) of diced tomatoes, stirring to combine. Bring the mixture to a gentle boil over medium-high heat.

Introduce 9 ounces of fresh cheese tortellini to the boiling broth. Reduce the heat to a simmer and cook according to package instructions, usually about 3–5 minutes, until the tortellini are tender.

Add 4 cups of fresh spinach into the pot, stirring until it's fully wilted and bright green, which should take about 1–2 minutes.

Taste the soup and season with salt and freshly ground black pepper to your liking, adjusting the flavors as needed. Serve hot in bowls, finished with a sprinkle of grated Parmesan cheese.