Preheat oven to 400℉. Line a large baking sheet with foil. Peel and cut the beets into thin wedges. Add to baking sheet and toss with 2 tbsp oil. Season with salt and pepper. Roast 25–30 min., until tender. With garlic press, crush the garlic cloves into a large bowl. Whisk in the vinegar, mustard, and remaining 5 tbsp oil until combined. Season with salt and pepper to taste. Add beets to vinaigrette, tossing to coat. When ready to serve, arrange the spring greens on a large platter and top with beet mixture. Drizzle any vinaigrette at bottom of bowl over greens. Garnish with the hazelnuts.