"A perfectly balanced pocket of vegetarian Buffalo delight. Great for parties or potlucks with people who can't eat meat but still want something packed with flavor. Flaxseed or barley tempeh work best. Choose a good brand of pitas that will hold together."
Place tempeh in a large bowl and cover with Buffalo sauce. Set aside to marinate, 10 to 20 minutes.
Remove tempeh from Buffalo sauce, reserving sauce. Heat oil in a large skillet over medium-high heat. Cook tempeh in a single layer, in batches, until heated through and lightly browned, about 3 minutes per side. Pour some Buffalo sauce back over tempeh to coat.
Combine blue cheese, cilantro, green bell pepper, celery, and onion in a large bowl. Mix in enough Greek yogurt until topping just holds together.
Divide tempeh pieces among pita pockets; top with a spoonful of the topping. Top with remaining Buffalo sauce.