Spawn NPC when you press a button

Can someone help me? I want to be able to spawn a NPC when you press a button in a VGUI. If anyone can help me, thanks.

[lua] function ShowTeamMenu()
local DermaPanel = vgui.Create( “DFrame” )
DermaPanel:SetPos( 50,50 )
DermaPanel:SetSize( 200, 250 )
DermaPanel:SetTitle( “Spawn an NPC!” )
DermaPanel:SetVisible( true )
DermaPanel:SetDraggable( false )
DermaPanel:ShowCloseButton( true )
DermaPanel:MakePopup()

local DermaButton = vgui.Create( “DButton” )
DermaButton:SetParent( DermaPanel )
DermaButton:SetText( “Zombie” )
DermaButton:SetPos( 25, 300 )
DermaButton:SetSize( 150, 50 )
DermaButton.DoClick = function ()
RunConsoleCommand( “ent_create npc_zombie” )
end

end
[/lua]