Preheat the oven to 275°F
Add the pistachios to a cutting board and chop finely. Add the feta and continue chopping as ingredients combine. Add parsley, dill, lemon zest, salt and pepper, and chop together to form a uniform mixture
Add salmon to a baking sheet, pat dry, season with salt and pepper, then brush top and sides with mustard. Add pistachio and feta mixture to the top, distribute evenly, and press lightly with a fork. Drizzle with olive oil and bake for 30-35 minutes until cooked through. Optional: broil for 1-2 minutes to brown the top
While salmon roasts, make tzatziki by draining liquid from cucumber using cheesecloth or paper towels. Add yogurt, strained cucumber, dill, mint, olive oil, garlic, lemon juice, salt and pepper to a medium bowl and mix to combine
Spread tzatziki on a plate, top with arugula, then top with a piece of salmon. Finish with honey and capers
