How to Make It
Light a grill. Brush the bread on both sides with 2 tablespoons of the olive oil and grill over high heat until toasted on both sides, about 2 minutes.
Meanwhile, in a large skillet, cook the bacon over moderately high heat until crisp, about 6 minutes. Drain on paper towels.
Spread the mayonnaise on the toast. Divide the salmon between 4 slices of toast and top with the bacon. In a medium bowl, mix the lemon juice with the remaining 1 tablespoon of olive oil. Season with salt and pepper. Add the watercress and toss. Mound the watercress on the bacon. Close the sandwiches, cut in half and serve.