package MyClass;
use Any::Moose;
use Foo::Heavy; # slows startup!
has foo => (is => 'ro', default => sub { Foo::Heavy->new });
##</code><code>##

sub foo {
    my ($self) = @_;
    state $foo;
    if (!$foo) {
        require Foo::Heavy;
        $foo = Foo::Heavy->new;
    }
    $foo;
}