In a bowl, mix together the sauerkraut and mustard. Spread over the flesh side of the salmon and press down firmly.
Heat the oil in a cast-iron or oven-safe pan over medium-high heat. Cook the salmon flesh side down for eight minutes. Flip the salmon over. Transfer the pan to the oven and bake for an additional eight minutes.
Divide the mixed greens and cucumbers onto plates. Top with the salmon and enjoy!