Remove pin bones and scales from flounder.
Put pretzels in a food processor and pulse into a fine dust. If needed you can sift to get rid of the big pieces. Coat flesh side of the flounder with the crushed pretzels and bake at 350 degrees for 10 minutes or until internal temperature reaches 145 degrees.
While fish is baking, put 1/2 cup maple syrup and 1 tablespoon of the mustard and a pinch of cinnamon into a pan on low heat and reduce. When the fish is done, drizzle a little of the maple mustard sauce on the fish and serve.