1. In a big bowl, mix steak, oregano, red pepper flakes, 1 tablespoon olive oil, 1 tablespoon lemon juice, 2 1/2 teaspoons garlic, and 1 teaspoon salt. Cover and leave to marinate at room temperature for at least 30 minutes or up to 2 hours, or refrigerate for up to 4 hours.
2. Meanwhile, in a small bowl, whisk together remaining 1 tablespoon lemon juice and 1/2 teaspoon garlic; add a pinch of salt. Let sit for about 20 minutes.
3. Add tahini, honey, 3 tablespoons olive oil, and 3 tablespoons water to the dressing. Whisk vigorously, adding more water as needed, until smooth and easily pourable; add salt and black pepper to taste. Set aside.
4. In a medium skillet over medium-high heat, add 1 tablespoon olive oil. Add orzo and cook, stirring, until golden, 3 to 5 minutes. Add broth and bring to a boil, then reduce heat to medium-low. Simmer, stirring occasionally and adding more broth 1/4 cup at a time if needed, until broth is absorbed and orzo is tender, 8 to 10 minutes; add salt and black pepper to taste. Cover to keep warm.
5. Fire up your grill for high heat; preheat for 5 minutes. Brush grates with oil. Thread 8 skewers with steak, onion, bell pepper, and tomatoes, alternating with 3 to 4 steak cubes per skewer. Drizzle kebabs with remaining 2 tablespoons olive oil; add salt and black pepper to taste.
6. Grill skewers, turning occasionally, until vegetables are tender and meat is cooked to desired doneness, 8 to 15 minutes total (grills can vary). Put kebabs on a plate.
7. In a big bowl, toss cucumbers and spinach with half of the dressing you set aside. Mix chives into the orzo mixture.
8. Divide salad and orzo into bowls; top with kebabs. Drizzle remaining dressing over bowls.