Angelica has been used as an aromatic herb in Scandinavia for millennia, and it is one of the few herbs to have originated in the North. It can be used in desserts, or, like here, with savory food like fish. If you cannot find fresh angelica, you can use other aromatic herbs, like lemon thyme and fresh bay leaves.
Pre-heat the oven to 390 Fahrenheit (200 Celsius).
Fill the belly of the fish with the angelica and a bit of the rhubarb. Put half of the salt in a large fireproof dish. Lay the fish on top, surrounded by the onions. Sprinkle the rest of the salt on top. You should make sure that both the onions and the fish are completely covered. Bake the fish in the oven for 25-30 minutes.
Place the remainder of the rhubarb in a small saucepan with a splash of water. Add the sugar, bring to the boil and allow the rhubarb to simmer until it almost collapses, but is still slightly chewy.
Scrape the salt off the fish. Remove the rhubarb and angelica from the belly of the fish and throw it away. Remove the skin, make incisions with a knife and lift out the fish pieces. Arrange the fish on plates with the baked onions, the rhubarb compote and the green salad.