1. Cut beef into small pieces. If necessary, and toss with Greek seasoning.
2. In a large skillet, heat oil over medium-high heat. Add beef, half at a time, and cook, stirring 2 to 3 minutes or until browned.
3. Divide beef among warmed pitas. Top with tomato, cucumber, and feta. Drizzle ranch dressing over filled pitas. Serve extra ranch dressing on the side, if desired.