Place Onion And Garlic In A Slow Cooker. Season Chicken With Lemon Pepper, Oregano, And Allspice; Place On Top Of Onions. Cover, And Cook On High For 6 Hours. In A Small Bowl, Stir Together Yogurt, Sour Cream, And Cucumber. Refrigerate Until Chicken Is Done Cooking. When Chicken Is Done, Fill Pita Halves With Chicken, And Top With The Yogurt Sauce