zola/docs/templates/shortcodes/gallery.html

{% for asset in page.assets %}
  {% if asset is ending_with(".jpg") %}
    <a href="{{ get_url(path=asset) }}">
      <img src="{{ resize_image(path=asset, width=240, height=180, op="fill") }}" />
    </a>
    &ensp;
  {% endif %}
{% endfor %}