Heat 1 tablespoon olive oil in a large pot over medium heat. Add the diced onion, carrot, and celery. Cook, stirring occasionally, until the vegetables soften and the onion becomes translucent, about 5-7 minutes. Add the minced garlic and sauté for another 1-2 minutes until fragrant but not browned.
Pour in 4 cups vegetable broth followed by the entire can of diced tomatoes with their juices. Stir in 1 teaspoon dried basil and 1 teaspoon dried oregano. Bring the mixture to a gentle boil, then reduce heat and let it simmer for 10 minutes to allow the flavors to meld.
Stir in the 9-ounce package of cheese tortellini. Cook according to package instructions, usually around 3-5 minutes, until the tortellini are tender and cooked through.
Add 1 cup fresh spinach to the pot and stir until wilted, about 1-2 minutes. Taste the soup and season with salt and pepper as needed.
Ladle the Tomato Basil Tortellini Soup (One Pot) into bowls. Sprinkle with grated Parmesan cheese if you like, and enjoy warm.
