Place cucumbers and red pepper flakes in a heatproof jar. In a medium sauce pot combine water, vinegar, sugar and salt and bring to a boil. Allow to cool slightly, then pour over the cucumbers. Set aside to cool.
Make the Wasabi Mayo:
Whisk all ingredients for the mayo together in a small bowl and refrigerate until ready to use.
Bake the Salmon:
Preheat oven to 375 degrees and line a baking sheet with parchment paper.
In a small bowl, combine lemon juice, herbs, olive oil and salt.
Place the salmon on a sheet of aluminum foil skin side down and cover with herb mixture and lemon slices. Cover with aluminum foil and bake for 15 to 20 minutes until cooked through. Slice into 12 pieces.
Place a new sheet of parchment paper on the baking sheet.
Slice the sweet Hawaiian rolls in half lengthwise. Remove the tops and set aside. Place the bottom half on the prepared baking sheet. Spread the mayo all over and top each one with a piece of salmon. Top with pickled cucumbers. Place the roll tops on top and brush with butter. Sprinkle with black sesame seeds and bake for 7 to 9 minutes, until warmed through. Serve immediately.