In a large skillet, cook beef over medium heat until no longer pink. Drain any excess fat, if any.
Stir in the tomatoes, Greek seasoning, garlic and pepper. Bring to a boil. Reduce heat and simmer for 8 to 10 minutes or until thickened. Add spinach and cook, stirring for 2 to 3 minutes, or until spinach is wilted. Add a splash of vinegar, if desired.
To make the tzatziki sauce, squeeze as much liquid out of the cucumber as you can. Combine sour cream, cucumber, and vinegar. Add salt and pepper to taste.
Warm tortillas and spread some tzatziki sauce on each one, then spoon some of the beef mixture into the center of each tortilla. Top with feta, diced cucumbers, and olives.