Grate the zest of 1 orange and the lime into a large bowl. Squeeze 1 tablespoon of juice from the grated orange and 2 tablespoons of juice from the grated lime into the bowl (you may need a second lime to get the 2 tablespoons of juice).
Whisk in the soy sauce and the oil. Set the dressing aside.
Use a sharp knife to slice the rind and pith from the remaining oranges. Working over a mixing bowl, cut between the membranes to free the orange segments, letting them drop into the bowl.
Pour any juice into a cup and reserve it for another use.
Add the mâche, frisée, and cucumbers, if using, to the orange segments. Using a large sharp knife, cut the salmon into 1/3-inch-thick slices.
Add the salmon to the bowl.
Drizzle with the dressing, and toss gently to coat. Allow the flavors to meld for at least 2 minutes.
Divide the salad among 4 serving plates.
Sprinkle with the toasted sesame seeds, and serve.