Preheat the oven to 410 dgrees Fahrenheit.
In a large bowl combine peeled and cubed sweet potatoes, beets, chopped red onion and 1 ½ tablespoons olive oil. Sprinkle with kosher salt and ground black pepper and mix gently to coat.
Line a large baking sheet with parchment paper (or aluminum foil) and spread the veggies in one even layer.
Roast for 30-35 minutes until the beets are fork tender and sweet potatoes lightly browned on the edges.
While the veggies are roasting, make the dressing using this Maple Balsamic Dressing recipe.
Once the beets, sweet potatoes and onions are out of the oven, leave them out to cool for at least 10 minutes.
Place spring mix (or other greens) in a large bowl or platter. Top with cooled roasted veggies, sprinkle chopped walnuts on top (you can toast them first, if you want) and drizzle with dressing.
Serve as is or toss the salad to distribute the dressing around right before plating.