How do I create a custom dashboard lens?

To create a dashboard lens you need to create a class that extends Aero\Admin\AdminLens and implement the data method:

class OrdersLens extends \Aero\Admin\AdminLens
{
    protected $title = 'Orders';

    protected static $permission = 'reports.orders';

    protected static $dateGetVariables = [
        'custom' => 'ordered-at-date',
        'start' => 'ordered-at-date-start-date',
        'end' => 'ordered-at-date-end-date',
    ];

    public function data(\Illuminate\Http\Request $request, array $date, array $compare): \Illuminate\Http\JsonResponse
    {
        $ordersCount = \Aero\Cart\Models\Order::visible()->whereBetween('ordered_at', [$date['start'], $date['end']])->count();
        $ordersCompareCount = \Aero\Cart\Models\Order::visible()->whereBetween('ordered_at', [$compare['date']['start'], $compare['date']['end']])->count();

        if ($ordersCompareCount !== 0) {
            $percentage = (($ordersCount - $ordersCompareCount) / ($ordersCompareCount > 0 ? $ordersCompareCount : 1)) * 100;
        }

        return response()->json([[
            'text' => number_format($ordersCount),
            'compare' => [
                'text' => $ordersCompareCount === 0 ? 'No data to compare' : $compare['text'],
                'percentage' => isset($percentage) ? ($percentage >= 0 ? '+' : '') . number_format($percentage, 2) . '%' : '',
                'up' => isset($percentage) ? $percentage >= 0 : '',
            ],
        ]]);
    }

    protected function link(): ?array
    {
        return auth()->user()->can('reports.view') ? [
            'route' => route('admin.report', ['key' => 'order-breakdown']),
            'text' => 'View Report',
        ] : null;
    }
}

Parameters