Toast the three slices of white bread until golden, then place them on a cutting board.
In a small bowl, mash together the Greek yogurt, cream cheese, minced dill and a dash of salt with a fork until smooth and well combined.
Spread about a tablespoon of the dill cream cheese mixture onto each piece of toast.
On one prepared toast, layer the torn butter lettuce and half of the smoked salmon.
Place a second piece of toast on top of the salmon with the spread side facing up, and sprinkle that spread with the capers if using.
Top the capers with the remaining smoked salmon, then add the sliced tomato.
Finish with the final slice of toast spread-side down to form the sandwich. Serve whole or cut into quarters and secure with toothpicks if desired.