stupid_function.cs

public static FieldViewModel GetField(this HtmlHelper<IEnumerable<FieldViewModel>> Html, string fieldId)
{
    FieldViewModel field = Html.ViewData.Model.SingleOrDefault(f => f.FieldId == fieldId);
    return field;
}

view.html

<div class="filter-wrapper">
@{
  var fields = Html.GetField("DesignationSK").Items.Select(i => new { i.ID, i.Label });
  var fieldsJson = Json.Encode(fields);
}
<label for="group">Group</label>
<input type="text" id="group" data-options='@fieldsJson'>
</div>