Heat grill to medium-high. Season the steak with 1/2 teaspoon each salt and pepper and grill to desired doneness, 3 to 5 minutes per side for medium-rare. Transfer to a cutting board and let rest for at least 5 minutes before slicing.
Place the corn on the grill along with the steak and grill, turning occasionally, until charred, about 3 minutes. Transfer the corn to a cutting board and remove the kernels from the cobs.
In a large bowl, whisk together the lime juice, oil, and 1/4 teaspoon each salt and pepper. Add the corn and onion and toss to combine, then fold in the avocados and cilantro.
Warm the tortillas on the grill. Serve with the steak, corn salad, and lime wedges, if desired.

Servers 6