Kosher salt and freshly ground black pepperto taste
For the Grill Pan
vegetable oilsuch as avocado oil or other neutral flavored, high heat oil
Instructions
For the Steak
Cut steak into into 1 1/2-inch cubes; set aside.
In a large bowl, whisk together olive oil, soy sauce, Worcestershire sauce, balsamic vinegar, honey, garlic, black pepper, thyme, smoked paprika, dried thyme and red pepper flakes (optional). Add steak cubes and toss well to coat; cover and refrigerate for at least 2 hours and up to a day in advance.
For the Vegetables
About an hour before you plan to assemble and cook the kebabs, add mushrooms, bell peppers, and red onion to a large bowl. Drizzle with 2 tablespoons olive oil and season with salt and pepper; stir until well coated. Cover and refrigerate for at least 30 minutes and up to 1 hour.
To Assemble and Cook the Kebabs
Add cast iron grill pan to cold oven and preheat oven to 425˚F. (recipe note #1)
Thread marinated beef cubes alternately with the vegetables evenly onto 6 skewers. (If using wooden skewers, soak them in water for at least 30 minutes beforehand to prevent burning.)
Remove preheated grill pan from oven with oven mitts, and brush lightly with vegetable oil. Arrange kabobs in a single layer on grill pan (they should sizzle when they touch the pan). Place in oven and cook 10-15 minutes, flipping kabobs halfway through cooking time, until the beef is cooked to your desired doneness and the vegetables are tender and slightly charred.
Remove grill pan from oven and transfer kabobs to platter. Let stand 5 minutes before serving.
Video
Notes
If you don't have an oven-safe grill pan, cook kabobs in a single layer on an oven-safe rack inside a foil lined rimmed baking sheet (or line a baking sheet with aluminum foil if you don't have an oven-safe rack). Increase the cooking time by a minute or two using this method.
Note that recipe time does not include marinating time, which can be anywhere from 2 to 24 hours.