Beef Skewers with Tahini Sauce

Ingredients

• ½ cup pineapple or papaya juice
• ¼ cup olive or vegetable oil
• 2 tablespoons soy sauce
• 1 tablespoon red wine or apple cider vinegar
• 4 cloves garlic, minced
• 1 teaspoon dried oregano
• ½ teaspoon freshly ground black pepper
• 1½ pounds sirloin steak, cut into 1½-inch cubes
• 12 small baby potatoes
• 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
• freshly ground black pepper
• 1 large, soft pita breads or lavash for serving
• ½ cup pure tahini paste
• 2 cloves garlic, very finely minced
• 6 tablespoons water, plus more if necessary
• ¼ cup fresh lemon juice, plus more to taste
• 1 teaspoon salt, plus more to taste
• ½ cup parsley leaves, very finely chopped