Ask your butcher to slice the steak to 1/4 to 3/8-inch thick.
Heat the grill. Combine the steak, seasoning mix, lime juice and oil in a zip-top plastic bag, turning and squeezing the bag to coat the steak evenly.
Arrange the steak on a surface; lightly spread 1/4 cup of the sour cream over one side of steak. Top with the bell pepper and onion; roll up and secure with toothpicks. Repeat with remaining steak and filling.
Grill the bundles, covered, over medium heat or coals for 8 to 12 minutes or to desired doneness, turning to grill all sides.
Remove the toothpicks; dollop with the remaining sour cream.