Had a discussion with D about this.
I think the g is silent. YEE-ro She says it’s pronounced with a hard g like gyroscope. Because it’s made on a spit that goes around.
Either way, it’s delicious.
Gyroscope is not with a hard g.JEYE roh scope
Gyro is pronounced as you described when speaking Greek, YEER-oh. In English, it’s generally pronounced JEYE-roh,although many use the Greek pronunciation.
While we’re being picky, gyros is the singular,
Soft G, more or less, though not with a long-i sound for the y. Jeeroh.
Year-O
I pronounce it the Greek way.
yeer-oh, rolling the r.
JEYE-roh
We were introduced to them by a Greek restaurant owner - an immigrant from Greece - who wouldn’t serve anyone who pronounced them incorrectly. 
Well, the first time he would, but not the second. He was very much loved in our college town and his gyros were second to none IME.
A different way every time! ?
This is one of those words I almost feel obligated to pronounce wrong or people are going to look at me funny. (Another one is foyer.)
What is the plural?
My son who works in food is adamant about using the Greek pronunciation.
year-ro
Like a cat hiss at the start, with the ''Y" blending in by a curl of the back of the tongue. Long e sound after the ‘r’.
So, kind of ‘HhyEE-ro’.
By pointing. Lol.
Lol …this is great. Jimmy Fallon did a funny parody on this exact question.
https://youtu.be/P9QOYYq3GkE
Don’t talk, just eat!!!
If we go in to a new place ordering gyros using the Greek pronunciation and the waiter doesn’t understand us, we change our order figuring we’ll be disappointed anyway. The fact that it happened a couple of times set our standard. The college Greek restaurant we started with set a pretty high bar for our tastes.
@Creekland. Wow, good strategy!. . Around here I’ve never ever heard it referred to as anything other than a Yeer-o. The first time I heard someone (during on the road travel) call it a Jy-ro I didn’t even understand that they were mispronouncing Gyro, I just had no idea what they meant. I guess it’s very dependent on where you live. When you live near a very large metropolitan area, I think the correct pronunciation is hard baked into most people’s vernacular.
Funny, I pronounce it “yeer-o” but at our favorite Greek restaurant, even they say “jie-ro” - probably because so many of the customers pronounce it that way.