1. Make the ability not channeled, and then flag it as transient.
2. Make it into a weapon and then set the flags up so it can fire while moving (see diamondback or phoenix) and set the chase and target filters appropriately.
3. Make it into a behavior that uses a periodic effect.
What you can't make it is a channeled (i.e. non-instant) ability as units can only have one current order at a time and if that order is to heal then it's not to move and vice versa.
There are a few ways:
1. Make the ability not channeled, and then flag it as transient.
2. Make it into a weapon and then set the flags up so it can fire while moving (see diamondback or phoenix) and set the chase and target filters appropriately.
3. Make it into a behavior that uses a periodic effect.
What you can't make it is a channeled (i.e. non-instant) ability as units can only have one current order at a time and if that order is to heal then it's not to move and vice versa.