How to Make It
In a large bowl, combine the salmon with the red and green bell peppers, scallions, heavy cream, Tabasco, kosher salt and pepper. Mix lightly but thoroughly.
In a small bowl, beat the egg white until stiff. Using a spatula, gently fold the egg white into the salmon. Form the mixture into 6 patties about 1/2 inch thick.
Preheat the oven to 300°. In a large skillet, heat 1 tablespoon of the oil until shimmering. Add 3 of the salmon burgers, sliding a piece of butter underneath each one. Cook the burgers over moderately high heat until well browned, about 3 minutes. Flip the burgers, reduce the heat to moderate and cook until well browned and just cooked through, about 3 minutes longer. Transfer the burgers to a cookie sheet and keep warm in the oven. Repeat with the remaining oil, burgers and butter.
Set a salmon burger on half of the nan. Top each with a heaping tablespoon of Green Tartare Sauce, a slice of tomato and 1/4 cup of the greens. Set the remaining nan on top and serve. Pass the extra tartare sauce at the tables.