my partner and i found ourselves in hayward on monday, and during a time of peckishness were pleased to find a taqueria that advertised tacos al pastor right there on the sign.
It's called El Castillito, and it is on Harder Rd about 1/2 mile west of Mission. That is about all I can tell you since I don't know hayward very well.
We checked it out first, and after determining that a) they do make the al pastor on a rotisserie and b) they dry-fry the meat before assembling your order, we ordered a torta al pastor to split.
We did this so that we could have a little room for later, but in fact this torta fed the two of us just fine for pretty much the rest of the day. It was on a crusty roll toasted both sides, and came with fresh avocado, tomatoes, lettuce and a slice of cheese. (I requested no cream.)
The al pastor was very good, spicy and smoky, and the texture and overall blending of flavors in the sandwich was very well done.
Best of all, it was a whopping $2.90 for a rather big sandwich.
Their menu is otherwise uninteresting, the usual array of tacos, quesadillas, and some egg dishes...kind of like an abbreviated Taq. San Jose. But if the torta al pastor is any indication (and I like to think it is), they do a fine job with their food. I'm not recommending anyone drive to Hayward to try them, but if you find yourself Hungry in Hayward, you'd do well to pay them a visit.