Make the chimichurri sauce by whisking together the olive oil, parsley, cilantro, red wine vinegar, lemon juice, onion, minced garlic, dried oregano, crushed red pepper flakes in a bowl. Season with sea salt and freshly cracked pepper, to taste. Set aside to allow flavors time to mingle.
Preheat your cast iron grill pan over medium-high heat until smoking hot, about 10 minutes.
Thread steak, zucchini coins, tomatoes, and red onion on the wooden skewers. Brush lightly with olive oil then season with sea salt and freshly cracked pepper, to taste.
Place 3-4 kebabs on your grill pan (don't overcrowd!) and cook for 3-4 minutes per side, or until the inside of the meat registers at 130-135 for medium-rare.
Remove from the grill pan and place on a cutting board then immediately brush the hot kebabs with some of the chimichurri sauce & loosely cover with a tin foil tent. Repeat the process with the rest of the kebabs.
Serve with the remaining sauce on the side. Enjoy!
Side Note: If you are using a grill: Heat the grill over medium-high heat to about 400 degrees. Cook the kebabs for 3-4 minutes per side, or until the inside of the meat registers at 130-135 for medium-rare.