1. Make the Tzatziki dressing: In a colander, toss together cucumber and 1 teaspoon salt. Place colander in sink, and let cucumber drain for 20 to 30 minutes. Press cucumber slices to extract excess liquid. Transfer to a bowl; mix in yogurt, garlic, dill, mint, oil, lemon juice, and remaining teaspoon salt. Refrigerate while preparing the sandwich fillings.
2. Toss the beef tips with Greek seasoning. Heat olive oil in a large skillet over medium heat and saute the beef until browned and cooked through.
3. Top each pita with the hummus, sautéed beef, onion, tomato and olives. Drizzle with Tzatziki dressing and serve.
To make the Tzatziki dressing, use the following ingredients:
1 medium cucumber, seeded and finely diced
2 teaspoons salt
1 cup plain (not fat free) yogurt
2 teaspoons garlic, minced
2 teaspoons fresh dill, finely chopped
1 teaspoon fresh mint, chopped
1 teaspoon extra-virgin olive oil
1 teaspoon fresh lemon juice