How to Make It
In a medium saucepan, cover the potatoes with water and bring to a boil. Season with salt and simmer over moderate heat until tender, about 15 minutes. Drain well. Press the potatoes through a ricer into the saucepan. Stir in the olive oil, vinegar, lemon juice and garlic and season with salt. Keep warm.
In a small bowl, whisk the lemon zest and lemon juice with the Dijon, oregano and marjoram. Gradually whisk in the 1/2 cup of olive oil until incorporated. Season the ladolemono with salt and pepper.
Light a grill and oil the grate. Season the fish with salt and pepper. Grill over moderately high heat, turning once, until the fish are white throughout, about 15 minutes total. Transfer the fish to plates. Serve with the ladolemono and skordalia.