Sauté the aromatics: Warm 1–2 tablespoons olive oil in a large pot over medium heat. Add 1 diced onion, 2 diced carrots, and 2 diced celery stalks.
Cook 5–6 minutes, stirring, until softened. Add 3–4 minced garlic cloves and cook 30 seconds, until fragrant.
Build the broth: Stir in 1 can (14–15 oz) crushed tomatoes, 6 cups low-sodium broth, 1–2 teaspoons Italian seasoning, and a pinch of red pepper flakes if using. Bring to a gentle boil, then reduce to a simmer for 10 minutes to let flavors meld.
Cook the tortellini: Add 12–16 ounces cheese tortellini.
Simmer according to package directions, usually 3–5 minutes, until just tender and floating. Avoid overcooking.
Add the greens: Stir in 4–6 cups baby spinach. Let it wilt for 1–2 minutes.
Turn off the heat.
Finish and season: Add 1–2 tablespoons lemon juice. Season with salt and black pepper to taste. Adjust heat or acidity as needed.
Serve: Ladle into bowls and top with chopped basil or parsley and a sprinkle of Parmesan, if you like.
Drizzle a little extra olive oil for richness.