Marinate and cook the steak: Combine jalapeño, garlic, cilantro, lime juice, oil, salt, pepper, and cumin in a large resealable bag or bowl. Add steak and toss to coat; if using bowl, wrap with plastic. Marinate in refrigerator overnight in refrigerator, tossing occasionally.
Bring meat to room temperature by removing from refrigerator for about an hour. Heat grill to 500 degrees and then lower to 400. Remove steak from marinade and grill about 4 minutes per side (depending on thickness) for medium rare. Generously brush the meat with the Texas Sriracha Sauce and turn the steak, sauce side down so the sauce will glaze. Only let this cook for about a minute. While the underside is glazing, generously brush the up-side of the steak with the sauce. Turn and repeat. Remove the steak and let it rest 10 minutes under foil before thinly slicing against the grain.
While the meat is resting warm tortillas in a microwave oven. Dampen a clean dish towel and wrap the tortillas inside. Place the package in a gallon sized plastic storage bag and place in microwave, without sealing the bag. Cook for 4 minutes on 50% power. Tortillas will stay steamy in the microwave until you're ready to use them. Divide steak among tortillas, then build with toppings.