Heat olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Add the Italian sausage, breaking it up with a spoon, and cook until browned and cooked through, about 5-7 minutes. Remove sausage with a slotted spoon and set aside, leaving drippings in the pot.
Add the diced onion to the pot and cook until softened, about 3-4 minutes. Add the minced garlic, oregano, thyme, and red pepper flakes (if using), and cook for another minute until fragrant.
Add the diced potatoes and chicken broth to the pot. Bring to a boil, then reduce heat to medium-low, cover, and simmer for 10-12 minutes, or until potatoes are fork-tender.
Return the cooked sausage to the pot. Stir in the heavy cream, sun-dried tomatoes, and Parmesan cheese. Simmer gently for 3-4 minutes until slightly thickened. Do not boil vigorously after adding cream.
Turn off the heat. Stir in the fresh spinach until just wilted. Season with salt and black pepper to taste.