Preheat the oven to 400°F.
Trim the Brussels sprouts, removing the hard ends and any discolored or wilted leaves.
Place the sprouts in a saucepan and cover with water. Add a pinch of salt. Bring the water to a boil. Boil the sprouts for 3-4 minutes or until they turn a bright green.
Drain the sprouts and rinse with cool water. Pat them dry. Cut in half.
Toss the sprouts in 1 tablespoon of olive oil, 1 tablespoon of nutritional yeast, ¼ teaspoon of salt, and ¼ teaspoon of pepper.
Place the sprouts, cut side down on a baking sheet lined with parchment paper. Using a drinking glass, smash the sprouts so they are slightly flattened.
In a small bowl, combine the additional nutritional yeast, cornstarch, lemon juice, olive oil, garlic powder, onion powder, salt, and pepper. Whisk together to form a paste.
Using a knife, spread the paste on the cut side of each Brussels sprout half. Place cut side down on the baking sheet.
Roast for 10-15 minutes. Keep an eye on the sprouts while baking to ensure they don't burn.
While the sprouts are roasting, whisk together the ingredients for the vegan honey mustard dipping sauce, and place in a small bowl for serving.
Serve the Brussels sprouts in a shallow bowl with the dipping sauce on the side.