In a large pot, heat olive oil over medium heat. Add the diced onion and sauté until translucent, about 5 minutes. Stir in the minced garlic, Italian seasoning, and red pepper flakes, cooking for an additional minute until fragrant.
Pour in the vegetable broth and diced tomatoes, bringing the mixture to a simmer.
Add the cheese ravioli to the pot and cook according to package instructions, usually about 4-5 minutes, until they float to the top.
Reduce the heat to low and stir in the heavy cream, chopped spinach, and Parmesan cheese. Cook for another 2-3 minutes until the spinach is wilted and the soup is heated through.
Season with salt and pepper to taste. Serve hot, garnished with fresh basil leaves if desired.