According to the description of the Full Metal talent, D.va should be healing 20% of the bonus damage dealt by her Fusion Cannons. However, going to Try mode, putting her at level 20 (50.4 basic attack damage, boosted to 75.6 with the Cannons) and attacking a Dummy, I see only 15’s pop up as healing numbers and am in fact healing 20% of ALL the basic attack damage against enemies where the Fusion Cannons are active (which isn’t just a visual bug, as I found by checking how fast I was healing) If it were as the description indicates, I should be healing 5 for each tick, not 15. So either the description or the talent needs a fix.
I think it means that it only heals when it deals bonus damage. Healing for only the bonus damage would be quite useless.