Combine barbecue sauce and chipotle peppers; reserve 3/4 cup sauce mixture. Brush some of remaining sauce mixture onto all sides of roast.
Place roast on grid over medium, ash-covered coals or over medium heat on preheated gas grill. Grill; covered 25 to 35 minutes for medium rare (135°F) to medium (150°F) doneness, basting roast with remaining sauce while grilling and turning occasionally.
To prepare Slaw, combine coleslaw mix, bell pepper, green onions, dressing and cilantro in medium bowl; toss to combine. Season with salt and pepper to taste. Refrigerate until ready to serve.
Remove roast when instant-read thermometer registers 135°F for medium rare; 150°F for medium. Transfer roast to carving board; tent loosely with aluminum foil. Let stand 20-25 minutes. (Temperature will continue to rise about 10°F to reach 145°F for medium rare; 160°F for medium.)
Carve roast across the grain into thin slices. Toss with reserved 3/4 cup sauce mixture. Evenly divide beef slices, coleslaw and tortillas among biscuits. Close sandwiches.