MyData.cs

using System;
using Unity.Entities;

[Serializable]
public struct MyData : IComponentData
{
    public float hoge;
}

MyEntity.cs

using Unity.Entities;
using UnityEngine;

[RequiresEntityConversion]
public class MyEntity:MonoBehaviour, IConvertGameObjectToEntity
{
    public void Convert(Entity entity, EntityManager dstManager, GameObjectConversionSystem conversionSystem)
    {
        var data = new MyData() {hoge = 2f};
        dstManager.AddComponentData(entity, data);
    }
}

MySystem.cs

using Unity.Entities;
using Unity.Mathematics;
using Unity.Transforms;
using UnityEngine;

public class MySystem : ComponentSystem
{
    protected override void OnUpdate()
    {
        Entities.ForEach((ref MyData mydata, ref Rotation rotation)=>
        {
            var deltaTime = Time.frameCount;
            rotation.Value = Quaternion.Euler(deltaTime*mydata.hoge, 0, 0);
        });
    }
}