Heat butter in a saucepot over medium heat. When it foams, add pasta and stir until golden. Add whites of scallions, rice and stock; bring to a boil, cover and reduce heat to simmer. Cook rice 15 minutes, add half the dill, peas and greens of onions. Stir, cook 2-3 minutes more then turn off heat.
Preheat broiler.
For the sauce, in small pot over low heat combine cream, crme fraiche, lemon juice, pickles, capers, salt, pepper and remaining dill. Keep at a low bubble while fish broils.
Dress fish with a little olive oil and season with seafood seasoning. Broil until opaque.
Wilt spinach over medium heat in drizzle of oil. Add garlic clove and season with salt and pepper.
Serve fish on a bed of spinach topped with warm tartar sauce and rice alongside.