How to Make It
In a food processor, combine 4 tablespoons of the butter with the tuna and red pepper and process to a coarse puree. Season with salt and pepper.
In a small skillet, melt the remaining 1 tablespoon of butter. Add the pine nuts and cook over low heat, stirring occasionally, until golden brown, about 3 minutes.
Spread about 2 teaspoons of tuna mousse on each toast and transfer to a platter. Garnish with the toasted pine nuts and serve.