Toast the sesame seeds in a skillet over medium heat until golden, shaking the pan, for 2 to 3 minutes. Transfer to a plate to cool.
Combine the sesame seeds, garlic, cola, soy sauce, brown sugar, sesame oil, 1 tsp salt and 1/2 tsp pepper in a large bowl, stirring to dissolve the sugar. Add the steak, onion wedges, and bacon, turning to coat. Cover and refrigerate for at least 4 hours and up to overnight.
Remove the steak, bacon, and onion wedges from the marinade with a slotted spoon. Heat a grill pan over high heat. If using the outdoor grill, make sure your charcoal is medium high heat. Put your onions, peppers, and bacon pieces in a grilling skillet or basket. Grill the onion wedges, peppers, and bacon pieces, turning until charred and brown, 8 to 10 minutes.
Grill the steak until charred, 4 to 5 minutes per side for medium rare.