Fry the almonds in a dry pan for 1-2 minutes, tossing occasionally until browned. Beat softened butter with the parsley, lemon rind, flaked almonds and ground pepper.
Place on baking paper, roll into a fat sausage shape using the paper to help you, and chill until required.
Heat grill until hot and lightly oil grill rack. Place trout on top and fill the cavities with lemon slices and a few sprigs of parsley. Grill fish for 3-4 minutes on each side.
When the trout is almost cooked, add a little of the butter mixture and flash under the grill until melted. Serve immediately with the rest of the almond butter, a handful of watercress and some thick-cut chips.