Preheat oven to 400 degrees. Line a baking sheet with foil.
Wash and peel beets. Cut into large chunks and place on prepared baking sheet. Drizzle with olive oil and sprinkle with sea salt and pepper. Toss to coat. Lightly pull foil up and over beets to create a pouch. Place in preheated oven and roast for about 40 minutes or until fork tender.
While beets are roasting, add all of your dressing ingredients to a small jar. Shake well until all the ingredients are incorporated. Set aside.
On a large platter or bowl, arrange mixed greens and red onions. Top with roasted beets and feta. Drizzle with salad dressing and enjoy!