Place chicken and 1/2 cup Italian dressing in a shallow dish or zip-top plastic freezer bag; cover or seal, and chill 30 minutes.
Remove chicken from marinade, discarding marinade. Grill chicken, covered with grill lid, over medium heat (300° to 350°) 4 to 5 minutes on each side or until done, basting with remaining 1/4 cup Italian dressing. Let chicken cool slightly, and finely chop.
Stir together chicken, cream cheese, salt, and pepper in a bowl.
Cut jalapeño peppers lengthwise down 1 side, leaving other side intact; remove seeds. Spoon 1 1/2 to 2 tablespoons chicken mixture into cavity of each pepper. Wrap each pepper with 1 bacon slice, securing with 2 wooden picks.
Grill stuffed jalapeños, without grill lid, turning frequently, over medium heat 20 to 25 minutes or until bacon is crisp.