- Preheat the oven to 425 degrees F. Lightly grease a sheet pan with oil. 
- In a large bowl, whisk together the tahini, olive oil, cumin, red pepper flakes, salt and pepper. Toss the cauliflower in the mixture. 
- Arrange the cauliflower in a single layer on a baking sheet. Roast for 20-25 minutes, flipping halfway through cooking, until browned. 
- For the soup, heat 1 tablespoon olive oil in a large saucepan over medium heat. Then sauté the onions until they start to soften, about 4-5 minutes.  
- Add the garlic, salt and pepper and cook for 30 seconds to 1 minute until fragrant. 
- Add the roasted cauliflower (saving 6-8 cauliflower florets for garnish), white beans, vegetable broth and parsley.  Bring the mixture to a boil. Reduce the heat and simmer for 10 minutes. 
- Carefully transfer the soup to a blender and puree until smooth. 
- Return the soup to the saucepan and warm low heat. Stir in the lemon juice. 
- Divide the soup into bowls. Top with the reserved roasted cauliflower and chopped parsley.