Depending on the recipe you could use a different seed or nut. Per tablespoon needed substitute equal amounts of one of these:
Black sesame seeds are most commonly used in Asian and Indian cooking. Just like their white (hulled) or brown (unhulled) counterparts they impart a nice nutty flavor. They may be raw or toasted to bring out the flavor. In Japan the sesame seeds are almost always toasted before using in a small pan (sesame toaster) with a screen lid made just for this purpose.
In Japan the seeds are mixed with salt then used to flavor rice or even added to sushi rice. They are also used in goma-dofu which is a special tofu with black sesame seeds. You'll also see them in most Shichimi Togarashi mixtures.