Dictionary<string, string> dir = new Dictionary<string, string>();
string splitOn = "value";
dir = cnn.Query<string, string, KeyValuePair<string, string>>("YOUR_SP", (s, i) => new KeyValuePair<string, string>(s, i), null, null, false, splitOn, null, null)
.ToDictionary(kv => kv.Key, kv => kv.Value);