Как вернуть custom json response в .net core web api?

View:

<h2>Home</h2>
<p id="contentId"></p>
<p id="contentValue"></p>
<script type="text/javascript">
    var request = new XMLHttpRequest();
    request.open("GET", "/Home/GetJson/?Id=" + 0);
    request.send();
    request.onreadystatechange = function () {
        if (request.readyState != 4
            || request.responseText == null) {
            return;
        }
        var obj = JSON.parse(request.response);
        console.log(obj);
        document.getElementById("contentId").innerHTML = obj.variable1;
        document.getElementById("contentValue").innerHTML = obj.variable2;
    }
</script>  

Controller:

public object GetJson(string Id)
{
    return new { Variable1 = Id, Variable2 = "Value"  };
}