ECS with UGUI Example

ECSandUGUI.cs

using Unity.Entities;
using UnityEngine;
using UnityEngine.UI;

public class PlayerHealthUIAuthoring : MonoBehaviour, IConvertGameObjectToEntity
{
    [SerializeField]
    TMPro.TMP_Text _uiText;

    public void Convert(Entity entity, EntityManager dstManager, GameObjectConversionSystem conversionSystem)
    {
        dstManager.AddComponentData(entity, new PlayerHealthUI
        {
            Text = _uiText
        });
    }
}

public class PlayerHealthUI : IComponentData
{
    public TMPro.TMP_Text Text;
}

public struct Health : IComponentData
{
    public int Value;
}

public class UpdateHealthUISystem : SystemBase
{
    protected override void OnUpdate()
    {
        Entities
            .WithoutBurst()
            .WithChangeFilter<Health>()
            .ForEach((PlayerHealthUI healthUI,
            in Health health) =>
            {
                healthUI.Text.text = health.Value.ToString();
            }).Run();
    }
}