Remove the skin from the trout, then remove the fillets of the bone, ensuring there are no bones left on the fillets.
Gently flake the fillets in to a bowl, add horseradish and season with pepper.
Cut avocado in half, remove seed and skin, cut flesh into slices.
Lay out four slices of bread and top with avocado slices, trout, cucumber and remaining bread.
Spread butter over the top of the bread, turn over and place buttered side onto a sandwich grill, spread butter onto the remaining side, close the grill and cook until golden.
Cut sandwich diagonally in half and serve.
Add a little chilli to the trout for extra spice.
Serving Size 4