Mabel's Steak Sammies

Step 1 -Preheat the grill to medium-high heat.

Step 2 -In a small bowl, add the onions, 2 tablespoons of the lemon juice, the salt, and the pepper and stir to combine. Allow the onions to marinate until ready to use.

Step 3 -In a second small bowl, add the balsamic vinegar, the whole-grain mustard, and the Dijon mustard and whisk to combine.

Step 4 -Evenly season the steak with the kosher salt and the black pepper.

Step 5 -Place the seasoned steak on the grill and cook until it reaches an internal temperature of at least 130 degrees F for medium-rare, about 2-3 minutes per side.

Step 6 -In the last 1-2 minutes of cooking time, evenly baste the steak with the balsamic mixture.

Step 7 -Transfer the grilled steak to a cutting board and let it rest, about 5 minutes, until it reaches 135 degrees F for medium-rare.

Step 8 -Thinly slice the steak against the grain.

Step 9 -Place the ciabatta halves on the grill and toast until they are lightly charred, about 1-2 minutes.

Step 10 -In a medium bowl, add the arugula, the olive oil, the remaining lemon juice, the salt, and the pepper and toss to combine.

Step 11 -Add the parmesan cheese to the arugula mixture and toss to combine.

Step 12 -On the cut-sides of the bottom ciabatta buns, evenly top with the sliced steak, the arugula salad, and the marinated onions. Discard the marinade from the onions.

Step 13 -Close the sandwiches with the top ciabatta buns and serve.