Top and tail the beetroot, peel and chop into bite size cubes. Add to a roasting tin and drizzle over the olive oil and season. Roast for 20 minutes.
Mix the herbs and spring onions together. Season the salmon fillets with salt and black pepper and then spread with the Dijon mustard.
Press the herbs and spring onion mixture on top. Reduce the oven to 200C/180C fan/gas 4. Nestle the salmon on top of the beetroot, add the wine, then cook for 15 minutes more and until the fish is cooked.
Heat the puy lentils according to the instructions on the pack. Remove the salmon and beetroot from the oven, set the salmon aside and mix the puy lentils and remaining parsley through the beetroot. Place the salmon back on top and serve.