Heat oven to 375°F. Spray cookie sheet with cooking spray.
Unroll dough; separate dough into 4 rectangles with 2 triangles each. Seal perforations to form each rectangle; place on cookie sheet.
Bake 8 to 10 minutes or until golden brown. Remove from oven; set aside to cool.
Meanwhile, in 10-inch skillet, place chicken, bell pepper and onion; sprinkle with garlic powder, salt and pepper. Cook over medium heat 12 to 14 minutes or until chicken is no longer pink in center and vegetables are soft. Remove skillet from heat.
Spread half of chicken mixture on 1 dough rectangle. Top with 3 slices of cheese. Place second dough rectangle over cheese. Repeat with remaining 2 dough rectangles and chicken mixture to make second sandwich. Place both sandwiches on same cookie sheet.
Bake 5 to 10 minutes longer or until cheese has melted. Let sandwiches stand 5 minutes before slicing and serving.