What size breaker and what size cable should be used.

Sounds like 10ga/30a to me. What do the instructions say?
A lot of times they say 8ga/40a no matter what oven is installed.

4100 VA / 240V = 17.0833333- Amps

As Greg has mentioned, #8 THHN CU. protected by a 40 Amp 2 Pole Breaker is "The Norm".

--Scott (EE)

It would probably live forever on 12ga and 20a breaker, even with the timer and the light inside but you should still be sizing at 125% of the calculated current. That is how I got to 10ga/30a.

Yes they only call for a 20ga and 20amp breaker but we are going with a 10ga/30amp and sleep well...'

Thanks