TO MAKE THE MARINADE

In a large glass or ceramic baking dish, whisk the Dr. Pepper with the BBQ sauce, brown sugar, mustard, hot sauce, vinegar and garlic. Add the flank steak and turn to coat thoroughly. Cover dish and refrigerate for at least 2 hours and up to 6 hours to marinate.

Preheat a grill.

Remove the flank steak from the marinade and pat dry with paper towels.

Brush the steak with canola oil and season one side of the steak with 1/2 teaspoon salt, 1/2 teaspoon steak seasoning and 1/4 teaspoon pepper. Flip the steak over and season second side with the remaining salt, seasoning and pepper.

Grill over moderately high heat, turning once, until the steak is medium-rare, about 8 minutes total. Transfer the steak to a work surface and let rest for 15 minutes.

While the steak is resting, pour the salsa verde into a large skillet and bring to a simmer over moderately high heat. Stir and simmer until slightly reduced, about 4 minutes.

Add the tortilla chips to the salsa and cook, stirring very gently, until the chips are soft but still slightly crunchy, about 2 minutes.

Stir in 1/4 cup of the cilantro and transfer the chilaquiles to a platter.

Thinly slice the steaks across the grain. Top the chilaquiles with the sliced steak and any accumulated meat juices. Scatter the avocados, Cotija cheese and remaining 1/4 cup of cilantro on top and serve immediately.