Wash and dry all produce. Halve, peel, and dice onion. Pick basil leaves from stems; discard stems. Remove sausage from casings.

Heat a large drizzle of olive oil in a large pot over medium-high heat. Add sausage, breaking up meat into pieces. Cook, tossing, until browned, 4-5 minutes per side. Add onion, garlic powder, and oregano to pot. Cook, tossing, until just softened, 2-3 minutes.

Add tomatoes, stock concentrates, and 5 cups water to pot. Stir, scraping up any browned bits from bottom. Bring to a boil, then season with salt and pepper.

Once soup is boiling, gently stir in tortelloni. Let cook until tender, about 8 minutes.

Stir spinach and basil into pot and let wilt. Season with salt and pepper.

Divide soup between bowls. Sprinkle with Parmesan and chili flakes (to taste).