Preheat oven to 400 degrees. Line a cookie sheet or sheet pan with parchment or foil. Toss the cauliflower pieces with 1 tbsp olive oil, salt and pepper.
Spread on the prepared sheet and roast in the oven for about 35 minutes or until golden brown, tossing the vegetables once midway through cooking time.
While the cauliflower is roasting, heat the vinegar and mustard seeds in a small saucepan over low heat for 5 minutes. Stir in the Dijon mustard, parsley, crushed red pepper, and olive oil. Keep warm.
Place the chickpeas, spinach and olives in a large bowl. Add the hot roasted cauliflower and warm dressing, tossing to wilt the spinach a bit and coat all ingredients lightly with dressing.