This simple and quick version of the dim sum favorite is a healthier, less greasy appetizer than the usual fried shrimp toasts.
Pulse shrimp, shallot, and ginger in a food processor until a coarse paste forms. Transfer to a bowl. Stir in mayonnaise, Sriracha, and lime zest and juice.
Heat broiler. Working in 2 batches, toast bread slices on a rimmed baking sheet 8 inches from heat source until golden brown, about 30 seconds. Remove from oven. Flip bread, generously brush tops with butter, and spread with a thin layer of shrimp paste (about 1 teaspoon each).
Broil until shrimp mixture is opaque and cooked through and toasts are browned, about 1 minute. Serve warm.
Shrimp paste can be refrigerated for up to 1 day. Baguette slices can be stored in an airtight container at room temperature for 1 day.