1. Clean the potatoes thoroughly, cut the cauliflower into small florets and cut the green beans in half.
2. Cook the vegetables in separate pots of boiling salted water until they are cooked al dente, about 15 minutes for the potatoes, 8 minutes for the cauliflower, and 5 minutes for the green beans and peas. Drain well.
3. Peel and finely chop the ginger.
4. In a large pot, heat the oil. Add the ginger and cumin, mustard, and sesame seeds. Fry until they are lightly browned and fragrant.
5. Add the vegetables and cook for 3 minutes. Add the lemon juice and season with pepper. Garnish with coriander before serving.