Heat 2 tablespoons of olive oil in a large pot over medium-high heat. Add the chopped onion and celery, stirring often, until the onion turns translucent, about 5 minutes.
Stir in garlic, Italian seasoning, and crushed red pepper. Sauté for 2 minutes, just until fragrant.
Add the beans, Parmesan rind (if using), vegetable broth, salt, pepper, and bay leaf. Bring everything to a rolling boil over high heat.
Lower the heat to medium-low and let the soup simmer gently, stirring occasionally, for about 20 minutes until the vegetables soften.
Discard the Parmesan rind and bay leaf. Carefully ladle 2 cups of soup into a blender. Remove the lid's center piece for steam to escape and blend until smooth, about 1 minute. Alternatively, use an immersion blender to blend partially.
Return the blended portion to the pot and stir. Add lemon zest and juice, mixing well.
Ladle the soup into bowls and garnish each with grated Parmesan cheese and fresh parsley, if desired.