Simmer the lentils in a pan of unsalted water until they are cooked but still have a slight bite. This will take about 40 minutes. Drain and set aside.
Meanwhile, make the sauce. Heat your oil in a frying pan and gently sauté the onions for five minutes. Add the sun-dried tomatoes and continue to cook for 5 minutes or so until the onions are softened and golden. Add the chilli, garlic and salt and continue to sauté for two minutes, stirring occasionally. Add the oregano, cumin and black pepper and stir fry for 2 minutes, ensuring the mixture does not catch.
Mix the sauce into the cooked lentils. Taste the dish and add salt as necessary, stirring well to ensure the salt is evenly distributed.
Cool and chill the lentil salad in the fridge until needed.