Combine stock ingredients with 750ml water in a large saucepan.
Bring to a boil, skim the surface, and simmer for 40 minutes.
Place a stainless steel bowl over a pan of boiling water without touching the water.
Whisk egg yolks and four tablespoons of water until pale and foamy for 6 minutes.
Slowly whisk in melted butter and season with salt, cayenne, and lemon juice.
Poach trout in the simmering stock for 6 minutes.
Add spinach, cucumber, and seaweed to the stock and cook for 3 minutes.
Serve trout on a bed of vegetables, topped with sabayon and fresh herbs.