Preheat oven to 375 degrees. On a rimmed baking sheet, toss cauliflower and garlic with 2 tablespoons oil; season with salt and pepper. Roast until cauliflower is tender and browned, 25 to 30 minutes. When garlic is cool enough to handle, remove peel.
In a food processor, combine cauliflower, garlic, beans, 1 tablespoon oil, lemon zest and juice, and 1/4 cup hot water. Process until smooth. Season to taste with salt and pepper. (To store, refrigerate in an airtight container, up to 3 days.) Serve drizzled with oil.
$0.67 per 1/4 cup