1. Preheat grill to 350° to 400° (medium-high) heat. Place chicken between 2 sheets of heavy-duty plastic wrap; flatten to 1/4-inch thickness, using a rolling pin or meat mallet. Sprinkle with seasoning and salt.
2. Grill chicken, covered with grill lid, 4 to 5 minutes. Add green onions to grill (if desired), and grill chicken and onions 4 to 5 minutes or until chicken is browned and done.
3. Snap off and discard tough ends of asparagus. Cook asparagus and next 2 ingredients in hot oil in a large nonstick skillet over medium-high heat, stirring often, 3 to 4 minutes or until asparagus is crisp-tender. Add capers and lemon juice; cook 1 to 2 minutes, stirring to loosen browned bits from bottom of skillet. Remove from heat; stir in dill and butter, stirring until butter melts.
4. Place chicken and onions on bread, and top with sauce.