Creamy Spinach Tortellini Soup

Ingredients for Creamy Spinach Tortellini Soup
1 tablespoon olive oil
1 small onion, diced
3 cloves garlic, minced
4 cups chicken or vegetable broth
1 (14-ounce) can diced tomatoes, with juice
1 teaspoon Italian seasoning
1/2 teaspoon crushed red pepper flakes (optional, for a bit of heat)
8 ounces cheese tortellini (fresh or frozen)
3 cups fresh baby spinach, roughly chopped
1 cup heavy cream (or half-and-half for a lighter version)
1/2 cup grated Parmesan cheese
Salt and black pepper, to taste
Optional Garnishes:
Fresh basil leaves
Extra grated Parmesan cheese
Crusty bread for serving