Peel and dice the sweet potato. Dice the peppers as well. Mix the dressing ingredients in a bowl and set aside. Cut the spring onions into slices.
Put the Tempo lentils with the cold vegetable stock in a small saucepan and cook for 10 minutes. Then let it soak for another 5 minutes and drain. Meanwhile, heat some oil in a large pan and fry the peppers and sweet potatoes for 3 minutes. Season lightly with salt and pepper. After 3 minutes stir in the curry powder and add a dash of water to the pan. Steam the potatoes while stirring until the water has boiled off. If the potatoes are not done yet, add a dash of water and let them cook again.
Finally, put the lentils, potatoes and spring onions in a large bowl and stir in the dressing.