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