Heat oven to 400°. On a rimmed baking sheet, toss Brussels sprouts with 1 tbsp of the oil, 1/4 tsp of the salt and the pepper. Roast at 400° for 15 minutes. Mix and roast another 10 minutes. If roasting at the same time as the cauliflower and broccoli, swap racks.
In a large bowl, whisk vinegar, remaining 1 tbsp oil, the mustard and remaining 1/4 tsp salt. Stir in roasted Brussels sprouts, pistachios and cherries. Season with freshly cracked black pepper, if desired.