Place the peas and fresh cold water in a pot. Set over medium heat. When it starts to boil, cook for 4 more minutes, then drain and return to pot.
Meanwhile heat a pan over medium heat and and sear the salmon. How long the salmon cooks depends on your preference: 2 minutes per side for rare; 4 minutes per side for medium rare; or 6 minutes per side for well-done.
When the peas are cooked and drained, mash them with butter, a pinch of salt and pepper, and some fish or chicken broth (you will need 1 cup).
Serve the fish over the pea puree. Finish by sprinkling with sea salt and grated lemon zest.