For the poached salmon:
1) Put the wine, water, bay leaves, parsley and of the sliced lemons into a large deep frying pan and bring to a simmer.
2) Add the salmon, skin side down. Add more water, if necessary, to cover the salmon. Cover the pan and simmer over a low heat until the fish is just cooked through, about 8 minutes.
3) Transfer the fish to a plate, cover it and chill it completely in the refrigerator, about 3 hours.
4) To serve, peel the skin from the fillet and scrape away any brown flesh. Put the fish on a serving plate, garnish with spring onion and the remaining lemon slices. Serve with Lemon Mint Tzatziki.
For the lemon mint tzatziki:
1) Line a strainer with paper towel and put the strainer over a bowl. Put the yogurt in the strainer and place it in the refrigerator to drain and thicken for 3 hours.
2) Seed and coarsely grate the cucumber. Drain it well. In a medium bowl, stir together the thickened yogurt and olive oil. Stir in the cucumber, lemon juice, garlic, zest and mint.
3) Season with salt and pepper, to taste, and serve.