Preheat oven to 400 degrees. Remove 1 garlic clove from 1 head, and very finely grate, setting aside 1/8 teaspoon. Wrap remaining heads of garlic in foil, and roast until very soft and golden inside, about 1 hour. Unwrap; let cool.
Meanwhile, whisk together grated garlic, lemon zest and juice, paprika, mustard, 1/2 teaspoon salt, and 1 teaspoon water in a small bowl. Squeeze roasted garlic from skins, and add 2 tablespoons to bowl, reserving remainder for another use. Stir to combine but leave very chunky. Stir in oil (do not completely incorporate).
Shave kohlrabi very thinly on a mandoline. Divide among 4 plates; season with 1/2 teaspoon salt. Spoon dressing over kohlrabi, then top with arugula leaves and almonds.
Using the cruciferous arugula -- instead of baby greens or other lettuce -- gives this salad a spicier flavor that complements the mild sweetness of the kohlrabi.