An class that allows generating plane meshes.

Plane.cs

using System;
using System.Threading.Tasks;
using UnityEngine;

/// <summary>
/// Plane class
/// </summary>
public static class Plane
{
	/// <summary>
	/// Create plane mesh
	/// </summary>
	/// <param name="resolution">Resolution</param>
	/// <param name="size">Size</param>
	/// <param name="pivot">Pivot</param>
	/// <returns>Plane mesh</returns>
	public static Mesh CreatePlaneMesh(Vector2Int resolution, Vector2 size, Vector3 pivot)
	{
		if ((resolution.x < 1) || (resolution.y < 1))
		{
			throw new ArgumentException($"Invalid resolution { resolution }. Resolution should be atleast { Vector2Int.one }.", nameof(resolution));
		}
		Mesh ret = new Mesh();
		Vector3[] vertices = new Vector3[(resolution.x + 1) * (resolution.y + 1)];
		int[] indices = new int[resolution.x * resolution.y * 6];
		Vector3[] normals = new Vector3[vertices.Length];
		Vector2[] uvs = new Vector2[vertices.Length];
		Parallel.For(0, vertices.Length, (index) =>
		{
			Vector2Int id = new Vector2Int(index % (resolution.x + 1), index / (resolution.x + 1));
			vertices[index] = new Vector3(((size.x * id.x) / resolution.x) - pivot.x, ((size.y * id.y) / resolution.y) - pivot.y, -pivot.z);
			normals[index] = Vector3.back;
			if ((id.x < resolution.x) && (id.y < resolution.y))
			{
				int offset = (id.x * 6) + ((id.y * resolution.x * 6));
				indices[offset] = index;
				indices[offset + 1] = index + resolution.x + 1;
				indices[offset + 2] = index + 1;
				indices[offset + 3] = index + 1;
				indices[offset + 4] = index + resolution.x + 1;
				indices[offset + 5] = index + resolution.x + 2;
			}
			uvs[index] = id;
		});
		ret.vertices = vertices;
		ret.SetIndices(indices, MeshTopology.Triangles, 0);
		ret.normals = normals;
		ret.SetUVs(0, uvs);
		ret.UploadMeshData(true);
		return ret;
	}
}