How can I replace the method being subscribed to in this line of code with a string variable?

Question

I'm trying to assign player inputs for new spells unlocked by a player, I'm using Unity's Input system. When a player selects a spell it subscribes the relevant binding to the spell's cast method (e.g. 'CastFireball()')

I want to replace the manual typing of "CastSPELLNAMEHERE()" on each spell with a string variable represented by _spellMethodID. I've been trying all sorts and googling from dawn to dusk and I can't get it to work. >:(

playerInput.FindAction(_spellID).performed += context => CastFireBall();

public void CastFireBall() { Debug.Log("fire"); }

I'd LIKE to be doing it like this instead:

string spell_methodID = "CastFireBall"
playerInput.FindAction(_spellID).performed += context => _spellMethodID;

public void CastFireBall() { Debug.Log("fire"); }

Help!