public List<MenuItem> MenuItems { get; set; }

protected void OnClickHandler(MenuItem item)
{
    if (item.ForceLoadUrl != null)
    {
        navManager.NavigateTo(item.ForceLoadUrl, true);
    }
}

public class MenuItem
{
    public string Text { get; set; }
    public string Url { get; set; }
    public string ForceLoadUrl { get; set; }
    public List<MenuItem> Items { get; set; }
}

protected override void OnInitialized()
{
    MenuItems = new List<MenuItem>()
    {
        new MenuItem()
        {
            Text = "site.css",
            ForceLoadUrl = "/css/site.css"
        },
        new MenuItem()
        {
            Text = "Counter",
            Url = "/counter"
        },
        new MenuItem()
        {
            Text = "Fetch Data",
            Url = "/fetchdata"
        }
    };

    base.OnInitialized();
}