Remove the outer yellow leaves from the Brussels sprouts and cut them in half.
Place sprouts on a foil-lined baking sheet. Drizzle with olive oil and season with salt and pepper. Bake for 20-25 minutes until browned and roasted, flipping halfway through the cooking time.
In a bowl, stir together mustard, honey, and onion powder.
Remove sprouts from baking sheet and toss with mustard mixture. Serve warm.