1. Squeeze juice from 1 orange and pour into a food processor or blender. Add garlic, cilantro, chiles and their sauce, oil, vinegar, cumin, coriander, and 1/2 teaspoon salt. Whirl until finely puréed.
2. Place steak in a 1-gallon zip-lock plastic bag. Pour cilantro-chipotle mixture over steak and seal bag. Chill at least 1 hour or up to 1 day.
3. Lift steak from marinade (discard marinade) and lay on an oiled barbecue grill over a solid bed of medium-hot coals or medium-high heat on a gas grill (you can hold your hand at grill level only 3 to 4 seconds); close lid on gas grill. Cook steak, turning every 4 to 5 minutes, until browned on both sides and done to your liking in center of thickest part (cut to test), about 12 minutes total for medium-rare. Transfer steak to a rimmed board or a platter. Let rest 3 to 5 minutes.
4. Thinly slice meat across the grain. Also slice remaining orange. Serve steak with orange slices to squeeze over servings, and add salt to taste.