Cook the Puy lentils according to packet instructions and drain.
Mix the lentils, sweet potato, herbs, breadcrumbs, nutmeg, and egg yolk in a bowl.
Place flour on a plate, beaten eggs in a bowl, and polenta on a separate plate.
Mould the mixture with floured hands into cylinders 7.5cm long.
Dredge each cylinder in flour, then egg, and finally polenta to coat.
Heat oil in a deep frying pan until a breadcrumb sizzles.
Fry the croquettes for 3 minutes until golden-brown and drain on paper.
Whisk the yoghurt, mint, lime zest, and lime juice together for the raita.
Serve the warm croquettes with the prepared raita dip.