Greek Pitas

1lb ground beef
1 can diced tomatoes, undrained
2 tsp Greek seasoning
1/2 tsp minced garlic
1/4 tsp pepper
2 cups fresh baby spinach (or about 1/2 cup frozen)
1/2 cup crumbled feta cheese
1/4 cup chopped red onion
1 package pita shells
olives, optional

In a large skillet, cook beef over medium heat until no longer pink; drain. Stir in the tomatoes, greek seasoning, garlic and pepper. Bring to a boil. Reduce heat; simmer for 8-10 minutes or until thickened. Add spinach and olives; cook and stir for 2-3 minutes or until spinach is wilted. Spoon into pita shells and top with feta cheese and onion.