Mix garlic, steak seasoning, smoked paprika, chipotle or cumin, hot sauce, Worcestershire sauce and vinegar. Whisk in extra-virgin olive oil. Place meat in shallow dish and coat it evenly in marinade. Let stand 15 minutes.
Cut leek in half lengthwise. Chop into 1/2-inch pieces. Place leeks in big bowl of water and release all the dirt from them with a good swish, separating all the layers. Drain leeks in a colander.
Grill flank steak 6 to 7 minutes on each side.
Put a drizzle of extra-virgin olive oil into a hot nonstick skillet over medium high heat. Cook bacon 3 to 5 minutes until it begins to crisp and has rendered most of its fat. Add leeks to the skillet and cook 3 to 5 minutes more until the leeks are tender.
Remove flank steak from grill and let juices redistribute before slicing. Thinly slice meat on an angle, cutting the meat against the grain. Serve sliced flank steak next to BLT potatoes and top potatoes with a dollop of sour cream.