Preheat oven to 425 degrees.
Cut head of cauliflower into somewhat evenly sized florets. Toss with 2-3 Tbsp. olive oil until well coated . Season with kosher salt and freshly ground black pepper. Roast, tossing occasionally to promote even browning, for 40 minutes
Toss rinsed chickpeas with 1 Tbsp. olive oil. Add to pan and continue to roast for 5 minutes. Remove tray from oven and place in a large bowl. Toss with vinaigrette. Sprinkle with parsley. Enjoy warm or at room temperature.
Mustard Vinaigrette: In small bowl, combine all vinaigrette ingredients. Whisk until well blended.