using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var s = "My test string is ##[FirstVal][SecondVal]##";
		var myvalues = Regex.Matches(s, @"##(?:\[([^][]*)])+##")
			.Cast<Match>()
			.SelectMany(m => m.Groups[1].Captures
              .Cast<Capture>()
              .Select(t => t.Value));
        Console.WriteLine(string.Join(", ", myvalues));
	}
}

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