use strict;
use warnings;
use Data::Dumper;

my %fields = (
    f1  => [ 1, 2 ],
    f2  => [ 3, 4, 5 ],
    f3  => [ 6, 7 ],
);

my @combinations = ( {} );

foreach my $field (keys %fields) {
    my @tmp;
    foreach my $value (@{$fields{$field}}) {
        foreach my $c (@combinations) {
            push(@tmp, { %$c, $field => $value } );
        }
    }
    @combinations = @tmp;
    print "Intermediate:\n" . Dumper(\@combinations);
}

print "Final:\n" . Dumper(\@combinations);