Using a mandolin with the guard, carefully slice cucumbers thinly and set aside.
In a medium bowl, combine tuna, onion, celery, Scotch bonnet pepper, lime juice and mayonnaise and mix thoroughly.
Season with salt to taste and garnish with paprika.
Spread Mustard and Chili Lime mayonnaise on slices of bread and place two slices of cucumber on top of each.
Generously spread tuna salad over cucumbers and top with the other slices of bread.
Remove crusts. Repeat with other slices and place on a plate lined with a doily.
Mustard and chili lime mayonnaise:
In the bowl of a food processor, combine all ingredients (except oil) and puree. With the motor running, gradually add oil. Taste and adjust seasoning. Because there are egg yolks in this recipe, this sauce does not store well. Make fresh and use it right away.