1. This step is optional, but this is what I usually do. Boil water in an electric kettle, place broccoli in a large bowl and pour half hot water over broccoli. Let stand for a couple of minutes, drain than finely chop.
2. Place cauliflower in the same bowl and repeat the process. Finely chop cauliflower.
3. Finely chop onion and cucumbers. Chop grapes.
4. In a large bowl, mix everything together.
5. Add mayo, lemon juice, salt and pepper. Mix well and enjoy!