Preheat oven to 400 degrees F
Wash the beets, pat dry, remove the greens (save them and sauté them!), and peel the beetroot with a vegetable peeler.
Chop the beets into cubes about 1 ½ inches in size
Spread the beet cubes on a baking sheet, drizzle the olive oil over and sprinkle with coarse salt
Roast the beets for 30-40 minutes, turning halfway through, until tender throughout
Spread the walnuts onto a small baking sheet and lower the oven temperature to 350 degrees F.
Toast the walnuts for 8-10 minutes, checking frequently to make sure they don't burn. I like to give the pan a shake every 3 minutes. You can also use the skillet method *see notes
Toss, in a large bowl the arugula, mixed greens, and goat cheese.
Add the roasted beets, walnuts and dressing to the salad, toss and serve.