Hmmm, after reading the card the answer seems obvious? (Though, that doesn't mean it has to be correct^^)
If Force Bash pushes a creature against a wall, will the creature still be slammed after the wall bash?
=> Card text: "Target receives the slam condition"
Or does the target have to actually leave the zone in order to be slammed?
=> It's not written on the card to be a prerequisite.
And if it does get slammed after wall bash, can you still slam another creature in the same zone?
Card text: "If target is pushed into a zone with other creatures, you may choose[...]"
Doesn't happen here. Thus you cannot give another creature slam.