For the cucumber-chile mignonette: In a medium bowl, stir together the cucumber, vinegar, mint, cilantro, shallot and chile pepper, and season with a pinch of sugar and a little salt. Refrigerate until well chilled, about 30 minutes.
For the shrimp salad: When ready to serve, combine the shrimp with the mignonette. Arrange the toasted baguette slices on a serving tray and top each with the shrimp and mignonette mixture.
Adapted from "My Perfect Pantry: 150 Easy Recipes from 50 Essential Ingredients" by Geoffrey Zakarian © Clarkson Potter 2014. Provided courtesy of Geoffrey Zakarian. All rights reserved.