Set up a steamer basket in a large pot of water and bring the water to a boil. Steam the cauliflower in the steamer for 5 minutes so the cauliflower is tender. Drain and then place in the fridge to cool.
Once the cauliflower has cooled, place it in a large bowl and add the remaining ingredients to the bowl. Toss everything together well, coating the broccoli in the mayo mix.