Rinse the snow peas, peel the kohlrabi and cut into thin slices. Rinse the leeks and cut into 1 cm-thick (approximately 1/2 inch) rings. Rinse and slice the fennel lengthwise. Rinse mushrooms and quarter if necessary. Rinse zucchini and cut into 1/2 cm (approximately 1/4 inch) slices. Rinse the carrots, thinly slice diagonally. Finely chop onion.
Sautée onion in oil, then add snow peas, leeks, kohlrabi, carrots and sautée briefly. Add 4 tablespoons of water, cover and let simmer just until tender.
Season the zucchini, fennel and mushrooms with salt and pepper, fry in 2 tablespoons of oil and mix with the drained vegetables.
Stir the oil, vinegar, orange juice, salt, pepper, sugar to make a dressing, pour over the salad, toss briefly and garnish with herbs.