After I had eaten my bread, I went to work. :tick:
After I ate my bread, I went to work. :tick: This is the best sentence. The tense is simple and balanced.
When I had eaten my bread, I went to work. :cross:
When I ate my bread, I went to work. :cross:
The above two sentences are not very good. They have another possible meaning, which is 'Whenever I ate my bread, I went to work. Whenever I didn't eat it, I didn't go to work.'
Probably the above example is not very likely to be misunderstood, but in some other circumstance confusion could exist with "When". The "After" sentences are much better.