Poaching salmon with lemon zest lends the fish a brightness that is only further highlighted by the crisp snow peas.
Bring water and lemon zest to a simmer in a large skillet. Season salmon fillets and add to pan with snap peas. Cover and cook 5 minutes, until salmon is opaque throughout; transfer to a platter. Drain and toss peas with butter, mint, and watercress. Drizzle with olive oil and season.