Thaw the salmon, wash, pat dry and season with a little salt and pepper. Fry in oil on medium heat until just cooked, then remove from the pan and keep warm.
Chop the onions and garlic cloves and sauté them in the pan. Deglaze with water and cream. Stir in the vegetable stock and tomato paste and simmer the sauce. Season with white wine, crème fraîche, salt and pepper.
Put the salmon back in the sauce and serve with rice.