Put the lentils in a deep saucepan and cover with cold water. Bring to the boil, skim off any scum that rises and then add the chilli and bay leaf. Simmer until the lentils are nearly soft (about 15 minutes), then add the carrot and cook for a further 5 minutes. Drain, discard the chilli and bay leaf, then tip the lentils into a bowl.
Fry the lardons on their own in a frying pan until the fat runs and they begin to colour. Add the garlic and onion and cook for 2-3 minutes until the onion begins to soften.
Tip this mixture into the lentils and toss well, then mix the dressing ingredients together and gently fold through the lentils. Taste and add salt and pepper. Rest the trout fillets on the lentils, scatter with the parsley and serve.