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

my $data1 = [
        { "shape" => "round", "food" => "apple" },
        { "shape" => "square", "food" => "pear" }
];

my $data2 = [
        { "big" => "cow", "small" => "bunny" },
];

my $combined;

foreach my $r (@{$data1}) {
        $r->{sizes} = $data2;
        push(@{$combined},$r); 
}

print Dumper($combined);