Place the beets in a saucepan and fill the pot with enough water to cover them completely. Boil for 25- 30 minutes, or until fork tender.
While the beets cook, make the dressing. Combine the oil, vinegar, dijon mustard, garlic, salt and pepper in a mixing bowl and whisk until well combined.
When the beets are fork tender, remove them from the water and drain. When they have cooled enough to handle, cut them into wedges, drizzle with some of the dressing and toss gently.
Put the mixed greens in a large mixing bowl and toss with the remaining dressing.
Arrange the mixed greens on the platter. Top with the beets, crumbled goat cheese and candied walnuts, and serve.