Combine soy sauce, sriracha, sesame oil, honey, and garlic powder in a gallon Ziploc bag. Zip closed and shake to combine. This is important: Pour about 1 tablespoon of the marinade into a small bowl to reserve it for later.
Add steak to Ziploc bag, remove all air, and seal so that the marinade can completely surround the meat.
Leave the steak to marinate at room temperature while you prepare the rest of the meal. Or, if you have time to marinate the steak ahead of time, keep it refrigerated in the marinade for up to 48 hours.
To make the snap peas, tear off a large piece of aluminum foil and place the snap peas in the center. Add the reserved tablespoon of steak marinade, pieces of butter (it will melt while the peas cook!), and salt over top. Fold up the aluminum foil around the peas, leaving a quarter-sized hole in the top for steam to escape.
To make the sesame slaw, place coleslaw mix in a bowl and sprinkle salt over top. Use your hands to massage the salt into the cabbage by crunching it tightly between your fists over and over for about 15 seconds, or until the cabbage begins to soften. Stir in sesame oil and lime juice and set aside.
To make the creamy sriracha sauce, stir together the mayonnaise, sriracha, lime juice, and salt. Set aside.
When you’re ready to eat, preheat an outdoor grill to medium-high heat (about 400 degrees F).
Remove steak from marinade and pat dry. Discard marinade. Grill for 4 minutes per side for medium-rare. Transfer steak to a cutting board and allow to rest for 10 minutes.
Add the snap pea foil packet to the grill and cook for 5 minutes total. Spray tortillas lightly with cooking spray and grill for about 30 seconds per side with the lid open, until charred but still soft.
Use tongs to carefully remove the snap pea foil packet from the grill. Carefully rip it open and transfer the peas and sauce to a bowl, add sesame seeds, and toss to coat in the soy-butter sauce.
Slice steak against the grain into very thin pieces. Top 4 to 6 tortillas with a few slices of steak, some slaw (toss it again to coat it in the dressing before you use it), sriracha sauce, a couple avocado slices, and a sprinkle of sesame seeds. Serve with snap peas.