Wash the potatoes and boil in water for about 20 minutes. Quench, peel and let cool down a little
In the meantime peel and chop the onion. Sauté in 2 tbsp. hot oil. Deglaze with 1/8 l water, bring to the boil and stir in 1/2 tsp. stock. Cut potatoes into slices and mix with the hot stock. Let stand for about 30 minutes
Clean and wash the leek and tomatoes. Cut leek into rings, cut tomatoes into eighths. Sauté leek in 2-3 tbsp. hot oil. Deglaze with a good 1/4 l water, bring to the boil and stir in 1 teaspoon broth. Cook the lentils for 8-10 minutes. Season to taste with salt, Sambal Oelek and vinegar
Mix the hot lentils with the broth into the potatoes. Fold in the tomatoes. Leave to soak a little. Clean and wash the salad and tear it into pieces. Season potato salad again and arrange warm on the lettuce leaves