Preheat the oven to 425 degrees F.
To rice the cauliflower, cut the head into large pieces that will fit in the feeder tube of a food processor, including the florets and stems. In batches, pulse the cauliflower until the size ranges from rice grains to about 1/4-inch.
On a baking sheet, toss half the chopped cauliflower with 1 tablespoon olive oil, curry powder, cumin, 1/4 teaspoon kosher salt and 1/4 teaspoon black pepper. Spread it into an even layer.
Roast the cauliflower for 10 minutes. Then stir it and continue roasting for 10 minutes until it's lightly browned and golden.
For the dressing, whisk the garlic, mustard, tahini, 1/4 teaspoon kosher salt, 1/4 teaspoon black pepper, lemon juice and 1/4 cup olive oil in a small bowl.
To assemble the salad, combine the roasted and raw cauliflower, apples, scallions, pistachios and parsley in a large bowl.
Drizzle with dressing, tossing to combine.