How can I get the ReturnType of an anonymous method passed as a parameter through reflection?

Let's say I have a simple class like this:

public class Employee
{
public string FirstName { get; set; }
public string LastName { get; set; }
public readonly Func<object> GuidGen;

public Employee(Func<object> guidGen)
{
    GuidGen = guidGen;
    var methodInfo = GuidGen.GetMethodInfo();
    var returnType = methodInfo.ReturnType;
    //ReturnType returns System.Object! not Guid
}
}

When creating an instance I pass an anonymous method that returns a Guid:

    var emp = new Employee(() => 
    {
        return Guid.NewGuid();
    }
    );
    var guid = emp.GuidGen.Invoke();

My question is, is it possible to get the ReturnType for the anonymous method I'm passing through the Employee constructor? When I debug I get a ReturnTypeof System.Object instead of Guid type.