2 large sweet potatoes (around 450 grams), scrubbed with salt and lots of freshly ground black pepper
A little vegetable oil
1/4 small red onion, very thinly sliced
1 Indian green finger chilli (chile), deseeded and finely chopped
1 tablespoon pumpkin seeds, lightly toasted in a pan until puffed up
2 large handfuls of watercress or rocket (arugula)
For the dressing:
2 teaspoons lemon juice
4 tablespoons mayonnaise, low-fat if you like
2 rounded tablespoons Greek yogurt
2 tablespoons extra virgin olive oil
1/2-3/4 teaspoon chaat masala
1 medium-small garlic clove, finely grated
1/2 teaspoon brown mustard seeds
1/2 teaspoon fennel seeds
Cut the potatoes into large wedges: the best way is to halve them horizontally and wedge each side. Place in a large pot of boiling salted water, return to boil and simmer until the tip of a knife goes through easily, eight to ten minutes.
Meanwhile, make the dressing. Whisk together the lemon juice, mayonnaise, yogurt, half the oil, the chaat masala and garlic; season to taste. Heat the remaining olive oil in a small saucepan, tilting it so the oil collects in one area. When hot, add the mustard seeds and reduce the heat. After five seconds, follow with the fennel seeds and cook until the mustard seeds pop, another few seconds or so. Stir into the dressing and season to taste.
Drain the cooked potatoes and, once dry, place on a hot oiled griddle and cook for one to two minutes on each side, or until the wedges have lovely grill stripes. Add them straight into the dressing with the red onion, green chilli and most of the pumpkin seeds and leaves. Toss well, garnish with the remaining seeds and leaves and serve.