In small bows, combine soy sauce, broth, ginger, and garlic. Divide the marinade into 2 medium shallow bowls. Place Tuna in one bowl and the bell pepper in the other. Turn the tuna and bell pepper to coat both sides. Cover and refrigerate for 15 minutes.
Coat grill rack orbroiler pan rack with cooking spray. Preheat the grill or broiler to medium.
Place the tuna and bell pepper on the prepared rack or pan. Discard the marinade from the tuna bowl. Griff or broil, basting occasionally with the marinade from the pepper bowl for 4 minutes per side or until the tuna is just opaque and the bell pepper are heated through and glazed.