PREHEAT oven to 350°F. Mix crabmeat, mayo, green pepper, carrots and mustard in small bowl; cover. Refrigerate until ready to serve.
UNFOLD pastry sheets onto baking sheets; brush evenly with egg white. Sprinkle with poppy seed. Cut each sheet into 18 (3x1-1/2-inch) rectangles. Do not separate rectangles.
BAKE 25 minutes. Remove pastry from baking sheets; cool completely. Separate pastry into rectangles. Split each rectangle horizontally in half. Spoon 1 Tbsp. of the seafood mixture onto bottom half of each rectangle; cover with top of rectangle. Serve salad in warm pastry.