Delegates/Events across threads

Hey everyone. I've tried looking this up on Google, but no luck. I don't know much about delegates and events besides the basics, so bear with me. Say I start another thread via QueueUserWorkItem(), and that thread calls an event upon completion. How can I have any code listening to that event execute in the main thread instead of the QueueUserWorkItem thread?

For example, this class starts a thread and fires an event from that thread.

 using UnityEngine;
 using System.Threading;
 
 class SomeClass : Monobehaviour {
     public delegate void SomeDelegate();
     public event SomeDelegate SomeEvent;
 
     void Start() {
         QueueUserWorkItem(new object);
     }
 
     void ThreadedProcess(object state) {
         //CPU intensive code here
         SomeEvent();
     }
 }

Then this class listens for that event.

 using UnityEngine;
 
 class EventListener : Monobehaviour {
     void Awake() {
         SomeClass.SomeEvent += ExecuteOnEvent;
     }
 
     void ExecuteOnEvent() {
         //I want this code executed from the main thread
     }
 }

ExecuteOnEvent() gets called from the QueueUserWorkItem thread. How can I have this method called from the main thread? Any help would be greatly appreciated :)