To make the dressing, put all the ingredients into a blender. Blend until the dressing is thick and combined. Check the seasoning, you may need more lemon juice.
On a large serving platter, arrange the spinach leaves, radish, cucumber, drizzle a little of the dressing over the top. Then arrange the trout slices and drizzle with remaining dressing.
Sprinkle the almonds on top and serve.