Preheat oven to 375. Fill a shallow baking dish with ¼-inch of water. Place the beets in the pan and cover the pan with aluminum foil. Bake for 1 hour and 15 minutes. Insert a knife to test for doneness. If knife does not go in easily, bake for another 15-20 minutes and check again. Allow beets to cool completely.
Peel the cooled beets and cut into ¼-inch slices. Cut each slice into quarters and set aside.
In a large serving bowl, layer the mixed greens with the shallots, beets, and feta. Pour desired amount of dressing over the salad, tossing until salad is evenly coated. Serve immediately.
Dressing
Whisk together the olive oil, vinegar, dijon mustard, salt, and pepper.
Recipe by at https://dev.gatheranddine.com/beets-shallots-feta-mixed-greens/