In a small jar with a tight-fitting lid, add the olive oil, vinegar, garlic, Dijon mustard, salt, and pepper. Seal the lid tightly and shake the jar for a few seconds, until the dressing is emulsified. Set aside.
Marinate the steak:
Cut the steak in half crosswise into two parts. This will make the ultra-long steak easier to handle and help it better fit on your grill. Blot the steak dry with paper towels.
In a small bowl, mix the marinade ingredients (olive oil, vinegar, hot sauce, salt, pepper, onion powder, garlic powder, smoked paprika, and ground cumin).
Rub the mixture on both sides of the steak, massaging it into the meat. Let the steak marinate at room temperature for 30 minutes.
Grill the steak:
Preheat your grill to medium-high and lightly grease it. Grill the steak for about 3 minutes per side for medium-rare (about 2 minutes per side on a dual-contact grill). (See notes).
Let the steak rest for 5-10 minutes before slicing.
Slice the steak thinly against the grain. Cut each piece crosswise into 2-3 smaller pieces, rotate each piece 90 degrees, and slice it. This way, you'll cut the tough muscle fibers, making the meat easier to chew.
Assemble the Salad:
In a large mixing bowl, add the arugula, red onions, and half the dressing. Mix to coat. Transfer the arugula and onions to plates.
Arrange the tomato slices around the arugula. Scatter the olives and goat cheese crumbles on top.
Top the salad with slices of steak. Drizzle with the remaining dressing and serve.
Video
Notes
Marinating the steak is a must. Skirt steak has tough muscle fibers, and a vinegar marinade helps break them down.
It's also important to slice this steak across the grain to make it easier to chew. Because the muscle fibers run along the width of this steak, you can't just slice it crosswise. Instead, cut it into manageable pieces, rotate each 90 degrees, and slice it.
Having said that, skirt steak will always be a little chewy. If you want a tender steak that doesn't require marinating (or cutting across the grain), use flat iron steak.
You won't be able to keep the dressed salad greens. They will wilt. But you can keep the cooked steak in the fridge, in an airtight container, for up to 4 days. Reheat the leftovers gently, covered, in the microwave at 50% power. Or enjoy them cold like you would cold cuts.
The USDA recommends cooking steaks to 145°F with a 3-minute rest.