Pierce the steak a few times with a fork. Toast the sesame seeds in a skillet over medium heat until golden, shaking the pan, 2 to 3 minutes. Transfer to a plate to cool.
Combine the sesame seeds, garlic, cola, soy sauce, brown sugar, sesame oil, 1 teaspoon salt and 1/2 teaspoon pepper in a large bowl, stirring to dissolve the sugar. Add the steak, onion wedges and bacon, turning to coat. Cover and refrigerate 4 hours or overnight.
Remove the steak and onion wedges from the marinade with a slotted spoon and transfer to a baking sheet. Heat a grill pan over high heat. Grill the onion wedges and peppers, turning, until charred, 8 to 10 minutes. Transfer to a platter. Grill the steak until charred, 4 to 5 minutes per side for medium rare. Add to the platter.
The marinated bacon is a tasty bonus to this recipe. Pat it dry and cut into ½-inch pieces. Cook the bacon until crisp and add it to one of our fried rice recipes for the perfect side dish.