In a deep skillet or saucepan, add oil and garlic and place over medium high heat. When the garlic becomes fragrant, add the florets, water, and a good pinch of salt and pepper. When the water starts to boil, cover, lower heat to medium, and cook for 15 minutes until cauliflower is tender. Check periodically, as all stoves are different, to make sure there is still water in pan. You need that water for steaming and for mixing later. Do not drain.
Using an immersion blender, blend everything together until smooth. Stir in lemon juice. Taste and season with additional salt and pepper. You can also transfer everything into a blender or food processor and blend or process until smooth.
If you find the cauliflower mash is too loose, simply continue to cook and stir in the pan until some of the moisture evaporates.