Peel the kohlrabies, cut into small cubes, and put in a large mixing bowl. Set aside while you make the dressing.
Put the yogurt, sour cream, mascarpone, garlic, lemon juice, and olive oil in a medium bowl. Add salt and pepper and whisk until smooth.
Add the dressing to the kohlrabi, followed by the fresh and dried mint and half the greens. Gently stir, then transfer to a serving dish (if desired).
Sprinkle the remaining greens on top, sprinkle all with the sumac, and enjoy!