Set the oven to 375 degrees. Season pork tenderloin generously with salt, heat a large drizzle of olive oil in a cast iron pan over high heat. Sear the tenderloin on all sides then place in the oven for 12 minutes, or until 160 degrees.
In a bowl whisk together mustard, brown sugar, and maple syrup.
When the pork is cooked, allow it to rest for 5 minutes then slice into thin slices. Divide the arugula between the slices of bread then top with goat cheese and pork tenderloin and drizzle with mustard sauce.