Cook the onions in the oil with ½ teaspoon salt in a large pot over medium heat, stirring occasionally, until softened, 4 to 6 minutes.

Add the tomatoes, chicken broth, and oregano, garlic, basil. Simmer until beginning to thicken, 10 to 15 minutes.

Transfer to a blender and puree until smooth (or use immersion blender)

Top with the croutons and Parmesan before serving.