Two alternatives spring to mind.

Rather than returning the list with GetBigList() return an iterator. So you would apply an operation something like:

my $i = $foo->get_big_list;
while (my $element = $i->next) {
    # do stuff to $element
};
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Alternatively, have a routine in your class that takes an anonymous subroutine and applies it to each element.

# in your class
sub apply_to_elements {
    my ($self, $coderef) = @_;
    $coderef->($_) foreach @{ $self->{'Big_List'} };
}; 

# somewhere else
$foo->apply_to_elements( sub {
  my $element = shift;
  # do stuff to $element
} );
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