First off, you shouldn't be giving your Oscar bread. They have such a wide variety of food for the Oscar that there is no need to give it human food.
Don't worry about what you are seeing. It's not choking, but is chewing and softening up the bread. Now, if the fish starts floating or something like this, then I would suggest to net the fish and use a small tweezers to remove the bread.
I don't think the fish is choking. I feed Oscars all the time with freeze dried krill and they do exactly what you described. It's just too big to swallow whole, but they just don't want to get rid of it.
Please ensure that you are taking proper care of your Wet Pets including a healthy and varied diet. Check out the links on Oscars.