Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a bowl, toss the Brussels sprouts and grapes with olive oil, salt, pepper, and garlic powder. Spread them evenly on the baking sheet.
1 ½ cup Brussels sprouts, ½ cup red grapes, 2 tsp olive oil, ¼ tsp salt, ¼ tsp pepper, ¼ tsp garlic powder
Roast for 20 minutes, stirring halfway through.
While roasting, toast the walnuts in a dry pan over medium heat for 2-3 minutes until fragrant. Set aside.
2 tbsp walnuts
In a small bowl, whisk together balsamic vinegar, Dijon mustard, and honey.
1 tsp balsamic vinegar, ½ tsp Dijon mustard, ½ tsp honey
After 20 minutes of roasting, sprinkle the toasted walnuts over the Brussels sprouts and grapes, then drizzle with the balsamic mixture. Toss gently and return to the oven for 5 more minutes.
Remove from the oven and serve warm.