Heat small saucepan over medium high heat. Add vinegar, sugar, mustard seed, salt, garlic and red pepper flakes to the pan and cook until it begins to simmer and sugar dissolves. Remove from heat.

Toss the dill, bay leaf, and sliced cucumbers together in a heat-proof bowl. Pour the simmering liquid over the cucumbers and stir to evenly coat. Allow to cool to room temperature or chill before serving. May be made up to 3 days in advance. Store in a covered non-reactive container in the refrigerator.