Does Moon Bard's Lunary Vitality apply to all targets of Mass Healing Word/Mass Cure Wounds?

I tried looking around for an answer on this, but haven't found anything yet. If it does, I feel like it would make this slightly underwhelming feature significantly better.

Lunar Vitality. Once per turn when you restore Hit Points to a creature with a spell, you can expend a Bardic Inspiration die and increase the amount of Hit Points restored by a number equal to a roll of the Bardic Inspiration die. The creature's Speed also increases by 10 feet until the end of its next turn.

I think there's two ways to read this:

Option 1) Once per turn when you restore Hit Points to a creature with a spell, you can expend a Bardic Inspiration die and increase the amount of Hit Points restored to that creature by a number equal to a roll of the Bardic Inspiration die.

Option 2) Once per turn when you restore Hit Points to a creature with a spell, you can expend a Bardic Inspiration die and increase the amount of Hit Points restored by that spell by a number equal to a roll of the Bardic Inspiration die.

I'd love some clarity on which reading is correct or if this is open to DM interpretation. 

The references to "once per turn", "a creature", and "the creature", seem to indicate that the intent is for it to only be usable on one creature, even if the spell heals more than one.

I agree that that's a little disappointing. In practice I'd probably allow it.