How can I use one method and also switch between a coroutine and the main method? [duplicate]

Question

Now I'm using two methods, one as StartCoroutine and one not.

What I want to do is to have just one method and when I set the StartCoroutine variable to true or false when the game is running I want it to switch between the coroutine and the main. Is there a simple way to do it with one method and not two, if not, how do I achieve this?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Grid : MonoBehaviour
{
    public GameObject gridBlock;

    public int worldWidth = 10;
    public int worldHeight = 10;
    public bool StartCoroutine = false;

    public float spawnSpeed = 0;

    void Start()
    {
        if (StartCoroutine)
        {
            StartCoroutine(GenerateGridSC());
        }
        else
        {
            GenerateGrid();
        }
    }

    private void GenerateGrid()
    {
        for (int x = 0; x < worldWidth; x++)
        {
            for (int z = 0; z < worldHeight; z++)
            {
                GameObject block = Instantiate(gridBlock, Vector3.zero, gridBlock.transform.rotation) as GameObject;
                block.transform.parent = transform;
                block.transform.name = "Block";
                block.transform.tag = "Block";
                block.transform.localPosition = new Vector3(x, 0, z);
            }
        }
    }

    IEnumerator GenerateGridSC()
    {
        for (int x = 0; x < worldWidth; x++)
        {
            yield return new WaitForSeconds(spawnSpeed);

            for (int z = 0; z < worldHeight; z++)
            {
                yield return new WaitForSeconds(spawnSpeed);

                GameObject block = Instantiate(gridBlock, Vector3.zero, gridBlock.transform.rotation) as GameObject;
                block.transform.parent = transform;
                block.transform.name = "Block";
                block.transform.tag = "Block";
                block.transform.localPosition = new Vector3(x, 0, z);
            }
        }
    }
}