Rinse the lentils well
Heat the oil in a medium pot, add the onions, garlic, and ginger; sauté until the onions are soft (~ 5 minutes)
Add a pinch of salt.
Add the cumin and cayenne pepper, and continue to cook for another minute or so, or until fragrant, stirring continuously
Add tomatoes, 3 slices of lemon, and the lentils, and broth. Stir well
Cover and bring to a boil.
Reduce the heat to low and simmer for about 30 minutes, or until the lentils are soft.
Squeeze in the rest of the lemon juice.
Serve hot topped with cilantro, green onions or parsley and a slice of lemon.