PREP: Preheat the grill to 450 degrees F. Once heated, clean the grill grates with a wire brush. Liberally oil the grill. (I do this by drenching a paper towel in canola or vegetable oil and, holding tongs, rubbing the paper towel over the grill.)
CORN: Shuck corn and discard the leaves and silk. Drizzle corn with olive oil and lightly sprinkle with salt and pepper. Rub the oil and salt/pepper into all sides of the corn. Add the corn to the heated and oiled grill over direct heat, and grill corn about 10-12 minutes total. Rotate every 3-4 minutes until brightly colored and lightly charred. Let grilled corn cool before cutting it off the cob and adding kernels to a large bowl.
STEAK: Prepare the rub by mixing together the garlic powder, ground coriander, cumin, paprika, chili powder, salt, pepper, and brown sugar. Remove the flank steak from packaging and blot dry with a paper towel. Drizzle 1 tablespoon oil on the top of the steak. Sprinkle half the rub on top and gently press in. Flip the steak over and drizzle the remaining 1 tablespoon of oil on the bottom of the steak and sprinkle on the remaining rub mixture. Gently press in. Place the spiced-rubbed steak directly on the grill and cook for 4-5 minutes per side, or until the internal temperature is 130-135 degrees F for medium rare or 145 degrees for medium. (I use a meat thermometer here. For a 2-pound flank steak, my grill takes exactly 4 minutes per side at 450 degrees F.) Remove the steak from the grill to a cutting board. Tent with foil and let it rest for 5-10 minutes. Once the steak has rested, slice it very thinly against the grain (See Note 1).
CORNTOPPING: Cut the avocado in half. Chop one half into small pieces and thinly slice the other half. Toss the grilled corn with the chopped avocado, thinly sliced green onions, finely chopped cilantro, minced garlic, and finely diced jalapeño. Add lime zest and lime juice, a sprinkle of salt, sprinkle of pepper, and gently toss together. Set aside.
SAUCE: Whisk everything together until smooth and combined. Add a pinch of salt and pepper to taste. Taste and adjust to personal preference (additional salt, pepper, sriracha, etc.)
TORTILLAS: Spray both sides of the tortillas with olive oil cooking spray and "grill" tortillas on the stovetop over the open flame until slightly charred. Alternatively, warm (covered with a damp paper towel) in the microwave. After tortillas have been warmed or charred, quickly fold them in half so they will fold easily when assembled.
ASSEMBLE: Fill up the grilled/warmed tortillas with thinly sliced steak, a generous spoonful of the corn-avocado mixture, and a spoonful of the sauce. Add in the thin slices of avocado. Additionally, add extra lime juice, cilantro, and/or cotija cheese to tacos if desired. Enjoy!
Video
Notes
Note 1: Steak grain: Find the fibers on the steak and determine how they are running along the steak. Once you find that grain, slice perpendicular (here's a visual). This will keep the meat juicy and tender. It's easier to chew when cut against the grain. If the meat strips are too long, cut them in half or chop for easier eating.Note 2: Chili: If you aren't a fan of spicy foods, I recommend using McCormick® chili powder and paprika; neither are very hot. I'd also recommend leaving out the jalapeño from the corn topping.