12 large cherry tomatoes (about the same size as the potatoes)
1 medium red onion, cut into chunks
1 tablespoon olive or vegetable oil
Kosher salt and freshly ground black pepper to taste
Large, soft pita breads or lavash for serving
Marinate the Steak: Combine the pineapple juice, oil, soy sauce, vinegar, garlic, oregano, and pepper in a glass container or zip-top bag. Add the meat, move around to coat, cover (or seal bag), and marinate in the refrigerator for at least 2 hours and up to 12.
Make the Tahini Sauce: In a large bowl whisk together the tahini, garlic, water, lemon juice, salt, and pepper. If it’s too thick, stir in additional water 1 teaspoon at a time until it’s the consistency of a thick salad dressing. Whisk in the parsley and set aside (or refrigerate in an airtight container for up to 1 week; bring to room temp and stir in a bit more water before using if necessary).
Make the Skewers: If using wooden skewers, soak 12 (6-inch) skewers 30 minutes before grilling (or use 12 metal skewers). Place the potatoes in a microwave-safe bowl, add ½ inch water, cover, and microwave until par-cooked, 8 to 9 minutes. Uncover, cool slightly, and drain. Combine the potatoes, tomatoes, and onions in a bowl and add 1 tablespoon oil and season generously with salt and pepper.
Preheat a grill or grill pan to medium high heat. Thread the meat, tomatoes, potatoes, and onions on the skewers and grill until the meat is cooked through and the vegetables are tender, 4 to 5 minutes per side. Throw the pitas on the grill for a minute to warm them up. Serve the skewers and pita along with the tahini sauce.