Combine the first 8 ingredients; cover and chill at least 1 hour. Spread each toast slice with 1/2 teaspoon cheese; top each with 1 tablespoon salmon mixture. Garnish with fresh dill sprigs, if desired.
You can prepare the salmon topping earlier in the day and keep it refrigerated until ready to assemble. These appetizers look great assembled like canapés; however, for a more informal get-together, you can set the toasts, cheese, and salmon mixture out and invite guests to build their own crostini.