Julienne the fennel and kohlrabi. Toss with the red onion and parsley.
Combine the olive oil and and lemon juice, drizzle on the dressing, and add a few pinches of salt and tons of pepper. Taste, adjust salt and acid levels.
Plate and give each serving a good squeeze of lemon juice, a pinch of red pepper flakes, and garnish with parsley and fennel leaves.