Quick n dirty function to convert a System.Json.JsonValue to an NSDictionary.

ToNSDictionary.cs

using System.Json;
...

var response = "{ \"foo\": \"bar\" }";
var jsonValue = JsonValue.Parse (response) as JsonObject;

// Split the lambda declaration and initialization
// so that we can do recursion;
Func<JsonValue, NSDictionary> toNSDictionary;
toNSDictionary = (obj)=> {

  var keys = new List<NSString> ();
	foreach (var k in jsonValue.Keys) {
		keys.Add ((NSString)k);
	}

	var values = new List<NSObject> ();
	foreach (var v in jsonValue.Values) {
		switch(v.JsonType) {
		case JsonType.String:
			values.Add ((NSString)(String)v);
			break;
		case JsonType.Array:
			values.Add (NSArray.FromObjects (((JsonArray)v).ToArray()));
			break;
		case JsonType.Object:
			values.Add (toNSDictionary (v));
			break;
		case JsonType.Number:
		case JsonType.Boolean:
			values.Add (NSNumber.FromBoolean((JsonPrimitive)v));
			break;
		default:
			throw new ApplicationException(String.Format("Could not convert JsonValue of type {0} to an NSObject.", v.JsonType));
		}
	}

	var dict = NSDictionary.FromObjectsAndKeys (
		values.ToArray(),
		keys.ToArray()
		);

		return dict;
	};

var nsDict = toNSDictionary(response);
Console.WriteLine (nsDict);