Preheat the oven to 425. Place a sheet pan in the oven while it preheats.
Add cauliflower to the hot sheet pan, add the oil and spices and toss to combine. Place in the oven for about 30 minutes, tossing halfway.
Make sure the beans are patted dry then roughly chop them, then place on a smaller sheet pan. Add the oil and spices and toss, then roast them for 15-20 minutes, until they are brown with crispy edges. Remove them from the oven and after 5 minutes of cooling, add the arugula and pistachios and toss together. Set aside.
While the cauliflower roasts, make the dressing. Add all ingredients to a jar with one of the tablespoons of water and whisk or shake to combine. For thinner consistency, add more water 1 teaspoon at a time and mix.
Remove the cauliflower from the oven, add the arugula and the onion to the sheet pan and toss.
Plate the salad, top with the crispy bean topping, then dress as desired and toss.
