Spread 1 tablespoon of the cream cheese on each of four slices of toast. Top each with capers, onion, greens, and a slice or two of tomato. Lightly salt the tomato, then add as much pepper as you'd like (this sandwich cries out for a lot of it). Finish by draping a few slices of smoked salmon over the tomatoes and topping with the remaining slices of toasted bread.