Soak cashews in a bowl of water overnight or for 8 hours. For a quick-soak method, pour boiling water over cashews letting it sit in the bowl for at least 45 minutes. Preheat oven to 400 degrees F and line two large baking sheets with parchment paper. Place chopped broccoli and cauliflower onto one baking sheet. Drizzle with 2 teaspoons oil and mix with hands until coated. Sprinkle with salt and pepper. Set aside.
Place a couple paper towels on the other baking sheet and spread out the drained and rinsed chickpeas. Place 2 more paper towels on top and roll the chickpeas around until completely dry. Drizzle with 1 teaspoon oil and roll around the chickpeas with your hands until they are all coated. Sprinkle with salt and pepper.
Roast the broccoli, cauliflower and chickpeas for 15 minutes at 400 degrees F. After 15 minutes, give the chickpea pan a gentle shake to roll them around in the pan. Roast both pans for another 10-15 minutes or until the broccoli and cauliflower are cooked through and the chickpeas are golden in color. Meanwhile, prepare the dressing by adding all dressing ingredients into a blender and blending on high speed until smooth.
When the vegetables and chickpeas are ready, remove from oven and place into a large mixing bowl. Add your desired amount of dressing on top and toss until coated. Season to taste. Serve over a warm bed of grains with more dressing drizzled on top.
The leftover dressing will keep for 5-7 days in the fridge in a sealed container. The dressing will thicken as it stands (especially when chilled) so you can add more water to thin out as necessary