Heat olive oil in a large pot over medium heat.
Add diced onion and sauté until translucent.
Stir in minced garlic and cook for 1 minute.
Pour in the broth and bring to a boil.
Add diced tomatoes and Italian seasoning.
Reduce heat to a simmer and cook for 5 minutes.
Add the tortellini and cook according to package instructions.
Stir in spinach or kale until wilted.
Season with salt and pepper to taste.
Serve hot, garnished with fresh basil.