Seared White Fish with Olive Relish and Lemon Mashed Potatoes

Place the potatoes in a large pot. Add enough cold water to cover and bring to a boil. Add 1 tsp salt, reduce heat and simmer until just tender, 15 to 18 minutes. Reserve 1/2 cup of the cooking liquid, drain the potatoes and return them to the pot. Mash with the lemon zest, 2 Tbsp oil, 1/4 tsp each salt and pepper, and 2 Tbsp of the reserved cooking liquid (adding more liquid if necessary). Meanwhile, in a medium bowl, combine the parsley, olives, almonds, lemon juice, garlic, red pepper (if using) and 2 Tbsp oil; set aside. Heat the remaining Tbsp oil in a large skillet over medium-high heat. Season the fish with 1/4 tsp each salt and pepper, and cook until golden brown and opaque throughout, 3 to 4 minutes per side. Serve with the mashed potatoes and relish.