Place the lentils and the stock in a large, heavy-based saucepan. Bring to the boil over a moderate heat, then reduce to a simmer and cook for 20-25 minutes until tender. If it looks like the lentils are drying out during cooking, add some water to the saucepan. Remove from the heat and drain once ready. Cover and keep in a warm place.
Preheat the oven to 220°C.
Line a baking tray with nonstick baking paper. Rub the salmon fillets with the groundnut and season with the paprika and salt and pepper. Bake for 10-12 minutes until just cooked; firm yet springy to the touch.
Stir the olive oil, sherry vinegar, mint and seasoning into the lentils. Spoon onto serving plates and rest a salmon fillet on top.
Whisk the Greek yogurt until smooth. Drizzle around the lentils and dress the plate with the rocket. Serve immediately.