Use event system instead of message system.

GazeGestureManagerForEvent.cs

using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.VR.WSA.Input;

public class GazeGestureManager : MonoBehaviour {
    public static GazeGestureManager Instance { get; private set; }

    public GameObject FocusedObject { get; private set; }
    GestureRecognizer recognizer;

    private void Awake() {
        Instance = this;

        recognizer = new GestureRecognizer();
        
        recognizer.TappedEvent += (source, tapCount, ray) => {
            if (FocusedObject != null) {
                //FocusedObject.SendMessageUpwards("OnSelect");
                ExecuteEvents.Execute<ISelectable>(
                    target: FocusedObject,
                    eventData: null,
                    functor: (target, data) => {
                        target.OnSelect();
                    });
            }
        };
        recognizer.StartCapturingGestures();
    }
	
	// Update is called once per frame
	void Update () {
        GameObject oldFocusObject = FocusedObject;

        var headPosition = Camera.main.transform.position;
        var gazeDirection = Camera.main.transform.forward;

        RaycastHit hitInfo;
        if(Physics.Raycast(headPosition, gazeDirection, out hitInfo)) {
            FocusedObject = hitInfo.collider.gameObject;
        } else {
            FocusedObject = null;
        }

        if(FocusedObject != oldFocusObject) {
            recognizer.CancelGestures();
            recognizer.StartCapturingGestures();
        }
	}
}