Add olive oil to a large stock pot and heat over medium.
Add the garlic and onion. Cook for 3-5 minutes until tender.
Add the red bell pepper and cook for another 2 minutes.
Add in the tomatoes, cauliflower, oregano, basil, red pepper flakes (if using), and salt. Be sure to submerge the cauliflower chunks in the tomato liquid as much as possible—it will seem like there is too much cauliflower, but there is just enough.
Bring the mixture to a boil. Reduce heat, cover, and allow the mixture to simmer vigorously for 25 minutes.
Turn off heat and purée mixture with an immersion blender for 5-10 minutes or until the mixture is very smooth. If you don't have an immersion blender, you can add the mixture to a blender in batches or a large food processor and very carefully blend (return soup to pan once done blending).
Add the nutritional yeast and more salt to taste. Simmer on low for an additional 10-15 minutes, stirring occasionally. If soup is thicker than desired, add in 1/2 to 1 cup water and whisk into soup.
Taste. If too acidic for your tastes, add a pinch of baking soda or a small drizzle of pure maple syrup to cut the acidity. Stir to incorporate.
Ladle soup into bowls. Drizzle with olive oil and top with chopped fresh basil, if desired.