I found my answer. The code below allows me to click anywhere in the highlighted (yellow) area when hovering over the menu (not just on the text):
<asp:Menu ID="m1" runat="server" Orientation="horizontal">
<StaticItemTemplate>
<div style="width:100%;">
<asp:HyperLink
ID="l1"
runat="server"
Text='<%# Eval("Text") %>'
NavigateUrl='<%# Eval("NavigateUrl") %>'
BackColor="Yellow"
Font-Underline="false" />
</div>
</StaticItemTemplate>
<DynamicItemTemplate>
<div style="width:100%;">
<asp:HyperLink
ID="l2"
runat="server"
Text='<%# Eval("Text") %>'
NavigateUrl='<%# Eval("NavigateUrl") %>'
BackColor="Yellow"
Font-Underline="false" />
</div>
</DynamicItemTemplate>
</asp:Menu>
<asp:Menu ID="m1" runat="server" Orientation="horizontal">
<StaticItemTemplate>
<div style="width:100%;">
<asp:HyperLink
ID="l1"
runat="server"
Text='<%# Eval("Text") %>'
NavigateUrl='<%# Eval("NavigateUrl") %>'
BackColor="Yellow"
Font-Underline="false" />
</div>
</StaticItemTemplate>
<DynamicItemTemplate>
<div style="width:100%;">
<asp:HyperLink
ID="l2"
runat="server"
Text='<%# Eval("Text") %>'
NavigateUrl='<%# Eval("NavigateUrl") %>'
BackColor="Yellow"
Font-Underline="false" />
</div>
</DynamicItemTemplate>
</asp:Menu>