So, tweeking the code you have above:

using System;
using System.Collections.Generic;
using System.Data;
using System.Text;

namespace Hire.Steverb
{
public static class SlimQueryResultsHelper
{
// Convert a result set in DataTable format to the format required by the Slim Query test table
public static List<List<List>> ConvertDataTableToObjectList(DataTable theTable)
{
List<List<List>> queryResults = new List<List<List>>();
foreach (DataRow row in theTable.Rows)
{
List<List> rowListOfColumnValuePairs = new List<List>();
foreach (DataColumn col in theTable.Columns)
{
List columnValuePair = new List();
object val = row[col];
columnValuePair.Add(col.ColumnName);
columnValuePair.Add(val == DBNull.Value ? "null" : val.ToString());
rowListOfColumnValuePairs.Add(columnValuePair);
}
queryResults.Add(rowListOfColumnValuePairs);
}
return queryResults;
}
}
}