Preheat the oven to 425°F (220°C).
Prepare the vegetables by chopping the sweet potatoes, Brussels sprouts, and red bell pepper.
Toss the chopped vegetables with olive oil, salt, and pepper in a mixing bowl.
Spread the vegetables in a single layer on a baking sheet and roast for 25-30 minutes, until tender and golden brown.
While the vegetables are roasting, cook quinoa according to package instructions and set aside to cool.
In a small bowl, whisk together olive oil and apple cider vinegar to form a dressing.
In a large bowl, combine the chopped kale, cooked quinoa, roasted vegetables, walnuts, and feta cheese if using.
Drizzle the dressing over the salad and toss gently to combine.
Serve immediately or let it marinate for 10-15 minutes for enhanced flavors.