Cut the leek for the garnish with a sharp knife into narrow strips.
Heat the oil for frying in a wok or possibly a heavy frying pan.
Add the leek rings to the wok or skillet and fry for 2-3 minutes until crisp. Set aside for later.
Heat the 3 tbsp peanut oil in the wok or skillet.
Add the yellow, green and red peppers and fry over high heat for about 5 min until the edges start to brown and soften.
Add the sliced water chestnuts, garlic and light soy sauce and sauté all the vegetables for another 2-3 min.
Transfer to warmed serving plates, garnish with the crispy leek rings and bring to the table.
You add 1 tbsp hoisin sauce in step 6.