Step 1: Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Step 2: Place the diced sweet potatoes, halved Brussels sprouts, and red onion wedges on the baking sheet. Drizzle with 2 tablespoons of olive oil and season with salt and pepper. Toss to coat evenly.
Step 3: Roast the vegetables in the oven for 25-30 minutes, tossing halfway through, until they are tender and have caramelized brown edges.
Step 4: While the vegetables are roasting, cook the farro in a medium pot with 3 cups of water or broth. Bring to a boil, then reduce heat and simmer for 20 minutes or until tender. Drain any excess liquid.
Step 5: In a small bowl, whisk together the remaining 1 tablespoon of olive oil, balsamic vinegar, honey, and Dijon mustard to create the dressing.
Step 6: In a large mixing bowl, combine the cooked farro and roasted vegetables. Pour the dressing over the top and toss gently to combine.
Step 7: Fold in the fresh parsley and optional feta cheese. Serve warm or at room temperature.