Combine cream cheese, chopped dill, horseradish, salt, pepper and lemon in a small bowl. Spread this mixture on the bread. Top with slices of smoked salmon. Use a heart-shaped cookie cutter (about 3 inches wide) to cut each bread slice into a heart. (Save the trim to nibble on for lunch the next day). Divide among two plates, sprinkle with red onion, garnish will dill, and serve.
Note: Heart-shape cookie cutters are sold at stores that sell kitchenware.