Toss the cauliflower with salt and pepper to taste and roast on a parchment-covered baking sheet in a preheated oven at 350 degrees for 25-30 minutes or until lightly golden and tender, but still crunchy.
Heat the oil in a saucepan. Add the garlic and herbs and saute for a minute.
Add the lima beans and salt and ground black pepper to taste, with 2 cups of water or vegetable stock. Let the lima beans come to a simmer, then remove half the beans and liquid to a blender along with 3-4 roasted cauliflower florets and blend until smooth. Be careful while blending hot liquids and follow your manufacturer's directions. If you have an immersion blender, you can certainly use this to blitz the beans right in the pot, but leave some beans whole for texture.
Add the remaining cauliflower to the pot and heat until the stew just begins to boil. Turn off the heat, check seasoning, and garnish with basil, if using. Serve hot with pasta or a crusty bread.