In a large Dutch oven heat 1 tablespoon olive oil and sauté 1 cup onion until softened.
Add the 3 cloves garlic (minced), cook 30 seconds.
Add 1 tablespoon Italian seasoning, 1 teaspoon salt, ½ teaspoon black pepper, 2 tablespoons tomato paste, 32 ounces chicken stock and 2 14.5 ounces cans diced tomatoes to the pot.
Bring to a boil then reduce to a simmer.
Add 1 lb frozen tortellini, 2 cups cooked chicken and 2 ounces baby spinach leaves and cook until pasta is tender (about 10 minutes).
Remove from the heat and stir through ½ cup heavy cream.
Ladle into bowls and sprinkle with ½ cup parmesan cheese, if using.