Oven suddenly tripping circuit breaker...bad oven or bad breaker?
My suspicion is that it is a faulty igniter (glow coil) in the oven.

I had the same problem with my NXR oven.  At first the circuit breaker would trip somewhat unpredictably while the oven was on.  I had a service technologist come out who could find nothing wrong with the oven.  After a few more weeks the circuit breaker started tripping fairly consistently after approximately 1-2 minutes of turning the oven on.  Each time before the breaker tripped, I could see that the igniter of the main oven was heating up normally as it got hot and started to glow orange.  The igniter is a glow coil that turns on as soon as you turn the oven on and that stays on as long as the oven is on. 

To pinpoint the problem, I tested several variations.  Turned the broiler on as this uses a separate igniter - This did not trip the breaker.  Turned the oven light and fan on without turning the oven on - This also did not trip the breaker.  Turned on other appliances that are on the same breaker circuit -  This also did not trip the breaker.  Based on all of the above, I deducted that the problem was most likely caused by the igniter of the oven.      

I bought this new igniter on amazon for $16 to replace the old one:

(http://www.amazon.com/gp/product/B001DPQN70?psc=1&amp;redirect=true&amp;ref_=oh_aui_detailpage_o02_s00)

There are several sites with instructions on how to replace an igniter in a gas oven.  I used this one:

http://ths.gardenweb.com/discussions/2288437/if-susan-fixed-her-nxr-oven-ignitor-u-can-2

Since I replaced the igniter, the oven has worked great and the circuit breaker hasn't trip anymore.

I think, although I was never able to confirm this, that after the igniter got hot (takes a minute or so), it somehow caused a short circuit.  I checked the resistance of the faulty igniter after removing it and it was normal (same resistance as new igniter).  Not surprising as I was checking the resistance when the igniter was cold and the circuits never tripped right away after turning the oven on when the igniter was still cold.