How can I get mesh to mesh intersection?

I use a little complex mesh to find out which monster is in my character's skill range.

And I also have a frame to fire the skill's damage.

So here is the question.

How i can get intersecting colliders(or meshes) with my character's skill range mesh?

I thought that using bound box is the way to go, but it intersect bigger size than I expected. (And even dont figure out intersection in editor - when not playing)

I already have the solution about this but it's crippy i think.

That is adding all monsters in OnTriggerEnter, and removing them in OnTriggerExit. Call GetHit() function when the fire frame.

Is there any substitute solution about this? or simply how can i know mesh to mesh intersection?(searched a lot but there isnt clear one)