In a non-stick frying pan, dry-fry onion and mince over a high heat for 2 mins, breaking up the mince as you go. Stir in the curry powder and lentils, pour in stock, then fiercely simmer for 10 mins.
While the mince is cooking, dice the tomatoes and roughly chop the coriander, then mix together in a small bowl. Put the naans briefly in a toaster to warm through, then pop one on each plate. Spoon a quarter of the mince over each naan, then top with a spoonful of the fresh tomato and coriander salad.