Cook beef, pepper & onion in skillet over med. heat until brown. Remove from heat and stir in bread crumbs, barbecue sauce and salt. Set aside.
Preheat oven to 375º. Separate crescent roll dough in 4 rectangles on lightly floured board. Roll dough in 8x4 rectangle-cut crosswise in half. Place 2 tbsp of meat mixture on each half. Top with some mozzarella. Pull corners of dough toward the center and twist. Pinch to seal. Place buns on greased cookie sheet. Repeat with rest. Makes 8 buns.
In small cup, beat egg yolk and 1 tsp water with fork until blended. Brush top of buns.