If uncertain about a term, just google for it. If there are many entries from native speakers chances are excellent that the term does exist.

roast (adj., attributiv) - Röst-

What kind of Rostzwiebeln??
Roast onions sounds like whole onions simmering deliciously around a leg of lamb, basting in the lamb fat, and browning sweetly.
Then you have
dried roast onions
which come in a shaker and which people throw over their salad (apparently) or I put them in bread dough to make onion bread

In addition to what you are looking for, please tell us where you are trying to get it. Restaurant/store? US/Canada/UK/Australia/NZ/Other?

Hab auf google pictures ein bild gefunden
http://www.markus-grasmueck.de/projekte/keiop...
also die Roestzwiebeln, die man auf ein hot dog packt. Ich bin gerade in USA, genauer Kalifornien und versuche in nem grocery store die dinger zu finden

Lis GB: dried roast onions klingt gut

How about french fried onions, then?
http://images.calorieking.com/branding/ck/run...

Although they might be battered, I am not sure.

If yes (or a starting place to look, anyway), it seems like they kept them in the grocery store near the canned soup or green beans (most popular use is to top a green bean cassarole). Maybe in the salad dressing section next to the croutons?

It seems to me they would be near the bacon bits (salad topping), shoestring potatoes or croutons, because they are all salad or soup toppers.

jnt, danke fuer die tips. die abgebildeten fried onions sind auch noch mit cheddar, Amerikaner moegen alles gerne mit Kaese, hab ich den Eindruck.

Mittlerweile hab ich die Hoffnung fast aufgegeben, hier meine gewuenschten Roestzwiebeln zu finden, weil die keiner wirklich kennt. Aber jedenfalls hab ich ein paar gute Vorschlaege fuer die Uebersetzung bekommen. Danke!

Back in Lauhbin my best friend's Ma used to make those, and she always called them "crissy crossy, bissy bossy, roasty onions". I thought she was crazy then, but eventually our local news agent picked it up, and sold them as crisps under the name of "CriCroBiBoRoO". It's life writing the best stories, ain't it?

'CriCroBiBoRoO' ?!!!?

GreGreLoLoYoMaMyDa

My impression is that "Röstzwiebel" are actually fried (in oil), rather than roasted. Like "Röstkartoffel" which are cooked in a frying pan.

It seems to me that what you are looking for is dried *fried* onions (taste nice but not recommendable for a delicate stomach).
The problem is that "Röst-" or "geröstet" is often mistranslated as "roast" or "roasted" (because it looks similar) although "roasted" actually means "(im Ofen) gebraten".

E.g. Schweinsbraten - pork roast; Sonntagsbraten - the Sunday roast ; Lammbraten - a roast of lamb, etc.
Roast vegetables - im Ofen gebratenes Gemüse.

Clearly "braten" can also be used for cooking in the pan, but "roast" only means cooking in the oven (usually in oil or fat).

This link gives a useful explanation of several English terms for different cooking methods. (Note though that in one place they have written "boiling" instead of "broiling" (similar to grilling).)

I note that LEO has "roast" included as translation for "rösten" (and vice versa) but this is not correct. Otherwise though, all of the LEO entries for "roast" are translated using a form of "braten".

Mary (nz/a)
But my German relatives call my roast potatoes Röstkartoffeln, they're definitely not Bratkartoffeln, so I would sometimes plead for Röst for roast.
I have a recipe for Röstzwiebeln, which says (translated basically) - cut into small pieces, spray with oil and roast in the oven until dry. I guess they could be fried and dried too. I have no idea how they are made commercially.

Finally, I found my precious "Röstzwiebeln" at Wholesome Choice which is a international grocery store in Irvine, CA (see http://www.wholesomechoice.com/about.htm). They're called "Fried Onions".

more precisely, they're called "Fried Onion", without "s"