public async Task<ActionResult> MyController(string Id) {
    . . . .
    MyModel model = new MyModel();
    var client = new ForceClient(instanceUrl, accessToken, apiVersion);
    var qry = await client.QueryAsync<MyModel.SFOpportunity>(
            "SELECT Name, StageName FROM Opportunity where  Id='" + Id + "'");
    model.Opportunity = qry.Records.FirstOrDefault();
    . . . .
return View(viewName, myModel);
}

public async Task<ActionResult> MyController(string Id) {
    . . . .
    MyModel myModel = await Task.Run(() =>
        {
            var result = new MyModel(Id);
            return result;

        });   // =====> Step 1
    . . . .
return View(viewName, myInfoView);
}

public class MyModel
{
    public SFOpportunity Opportunity { get; set; }
    public MyModel(string id)
    {
        setOpportunityAsync(id);
    }

    private async void setOpportunityAsync(string id)
    {
        . . .
        var client = new ForceClient(instanceUrl, accessToken, apiVersion);
        var qry = await client.QueryAsync<MyModel.SFOpportunity>(
             "SELECT Name, StageName FROM Opportunity where  Id='" + id + "'");  // ======>  Step2
        Opportunity = qry.Records.FirstOrDefault();  // =====> step3
    }

public class HasConstructorWithAsyncCall
{
    public HasConstructorWithAsyncCall()
    {
        MarkConstructorFinishedAsync();
    }

    public bool ConstructorHasFinished { get; private set; }

    async void MarkConstructorFinishedAsync()
    {
        await Task.Delay(500);
        ConstructorHasFinished = true;
    }
}

[TestMethod]
public void TestWhenConstructorFinishes()
{
    var subject = new HasConstructorWithAsyncCall();
    Assert.IsFalse(subject.ConstructorHasFinished);
    Thread.Sleep(600);
    Assert.IsTrue(subject.ConstructorHasFinished);
}