Za'atar and yogurt pair magically to create a healthy and full-flavored dressing in this easy asparagus recipe. A spice blend of sumac, sesame and herbs, za'atar is a middle eastern staple available in middle eastern markets and where other specialty spices are sold. To make your own: blend 1 teaspoon each ground sumac, sesame seeds and dried thyme with 1/4 teaspoon salt.