In a small bowl, whisk together the mayonnaise, The Holly Tree Organic Yellow Mustard Powder, and lemon juice until smooth.
Add the chopped hard-boiled eggs, The Holly Tree Organic Black Pepper Powder, The Holly Tree Organic Parsley Leaves, and Salt. Mix gently until the eggs are evenly coated.
Toast the bread slices until lightly golden.
Place a lettuce leaf on two slices of bread.
Spoon the mustard egg mixture evenly over the lettuce.
Top with the tomato slices and cover with the remaining bread slices.
Slice each sandwich diagonally and serve immediately.