Let's start with the rules. Disciple of Life sets out 3 conditions:
- use a spell
- 1st level or higher
- to restore the health of a creature
Healing spirit is a spell of 1st level or higher That you can cause (be used to restore life points. He almost fulfills word for word the conditions required for Disciple of life. Here's how it works.
Addressing certain concerns
This should not work as no action is required to restore the hit points.
Disciple of Life doesn't require you to use an action, it doesn't mention the economics of action at all.
Also, as @jgn pointed out, it is worth noting here that Disciple of Life does not fire when you cast a spell, but every time you use it to restore health. (This is somewhat unusual as many features are triggered when casting a spell, but it is an important distinction.)
It is not the character but the spirit that causes healing.
The spirit is not a creature, it is not designated as a creature or anything that would have an impact or mechanical action in the game in addition to healing and moving what you make him do it. This is how the spell takes effect. You are not commanding a spirit to do something, you are making a physical manifestation of a spell do it. If the spell summoned an elemental creature that could in turn heal, this argument would make sense, but that is not what the healing spirit does.
A similar argument could be made for goodberry (you do not restore hit points, eat the berries), but it was made clear in the Sage Advice Compendium (which contains official decisions on how to interpret the rules) that Disciple of Life works, in fact , with the goodberry to spell:
If I am a cleric / druid with the Discipleship of Life function, does goodberry out benefit from the functionality? Yes. The Disciple of Life feature would force each berry to restore 4 health instead of 1, assuming you cast goodberry with a 1st level spell slot.
Healing spirit is too strong.
Ultimately, it is the DM who manages the game. If they feel that the healing spirit is too powerful, they can ban it or change it to make it less powerful .
If so, I suggest changing the spell text to:
Once per turn until the spell ends, each time you or a creature you can see movements in the mind space for the first time during a turn or begins there in turn, you can cause the spirit to restore 1d6 health to this creature (no action required).
(highlighted text added by me)