Normally when staying in Oudomxay I would have dinner at the Sinphet restaurant (N20 41.288 E101 59.182 - opposite the Boualy Tyre and Tyre Repair shop). Not that the food was that great but there were always fellow travelers swapping stories about their Lao experiences. However, the Sinphet seems to have downsized/closed.
This time I had dinner at the Kanya Restaurant (N20 41.359 E101 59.111) which is located in a small road off the main road (Rd 13N). Great food and good service but can be quite busy in the evening time at least it was when I had dinner there.
A good place for breakfast is Siso bakery on the main road. However, they have moved from their old place next to Samlaan Cycling Tours to a place a bit further south on the other side of the road - Coordinates: N20 41.142 E101 59.252
(next time I am passing through Oudomxay I will take pictures of the 2 places)