The case has been made already; I just want to point and laugh at the OP for complaining about people pronouncing it incorrectly when he didn’t even make the correct pronunciation one of the options (thus we can reasonably assume he didn’t even know what the correct pronunciation was). You should be properly shamed.
What he said. Or, rather, what he typed.
I wouldn’t begrudge someone in Ireland or England “mispronouncing” this word, much less quesadilla–but I assume everyone understands what they mean when they say it, right?
Which “a” is that? The one in father, the one in hate, or the one in cat?
If we refer to English vowel sounds by standard (printed) letters–which have no intrinsic sound–it can get confusing. Even if you use terms like “long a, short a” etc., that falsely presumes that there are only 10 vowels in English, and ignores that word stress affects “vowel” production. Even if you want to pronounce the Spanish vowel in question here it can vary amongst speakers, ranging in openness between /Ɛ/ (the English vowel in get) and /ei/ (as in English cake). It makes sense that some English speakers might tend toward that later, as that phonology is probably more common in English, doesn’t it?
Well, to get nitpicky, I pronounce it differently depending on if I am speaking English or Spanish. In English, I use the English “h” for “j,” and anglicize the vowels: first a is short as in “hat,” the e pronounced as a long English “ay.” Ha-luh-PAY-nyo.
If I am speaking Spanish, I pronounce the"jota" with a bit of a guttural sound and use the proper Spanish vowels, which are more clipped than English vowels. (j)ah-lah-PEH-nyo.
Why does everybody insist on putting a Y behind the E anyway? MeanOldLady is right. PEY, PAY, PEI etc. are all wrong. It’s PE.
If you can pronunce words like BED or RED, then it shouldn’t be impossible for you to pronounce an /e/ without appending an /i/.
Because, by English vowels rules, if a vowel is left open (that is, not followed by a consonant), it is pronounced long. So “pe” is pronounced “pee,” like “he,” “she,” “be,” etc.
Better yet, what’s the pronunciation of “Pronounciation”?
'nother vote for this one, which is about as closer as a gringo can be expected to get to the Mexican/spanish pronunciation.
Interestingly, I had an elderly friend who hailed from Texas (northern Texas that is, a long way from the border). He always used the hillbilly pronunciation…jap-a-LEE-na. I guess that was the way he’d learned to say it. I have no idea whether that abomination is common usage in the midwest.
SS
Grr. My husband did the same thing, turning it into ja-LOP-pen-O. This was all fine and dandy until someone got hurt. Me. As we were standing in public and I used his stupid pronunciation and I think the whole store stopped just to look at the stupid woman who can’t pronounce jalapeno. Grr.
And another.
CHI pol TAY
no really, hal-a pain-yo
Other. Hal-ah-PEE-nyo.
Chi-POTE-lay. 
Well, I knew how to correctly pronounce it, but wasn’t sure where to put the “y”, and all the while the *&^%$#@ 5 minute timer was ticking. Sue me. 
ha la Pei nyo
you forgot the tilde over the n
Trailer Park Boys debate this very question:
This is exactly what you have done, in your two examples.
It’s ha-la-PAY-nyo.
I’ve only ever heard Chipotle pronounced as something like “Chi-Pote-Ill”, but Australia and New Zealand aren’t noted for its Spanish-speaking population (or proximity to a significant Spanish-speaking country), which also probably explain the common (at least IME) presence of pronunciations like “Hal (or Jel)-a-Peen-O” and “Kwes-A-Dilla”.
Yes, a disturbing number of people in this part of the world appear to have attended the Zap Brannigan School Of Foreign Languages.
I worked with a girl from Iowa who said ‘tor-till-ee-a’.
As others have said, “Other”
I tend to pronounce it either Hah-lah-pehnyo (last two sylables slurred together, versus the first two being distinct) or kHa-lah-pehnyo (same thing, but a harder “H” sound). It’s the ñ that trips the white folks up.