How do I render specific child entries of a structure based on url segment
Probably the simplest way is to split the code up like this in your template.

{% switch entry.level %}
    {% case 1 %}        
        {# all the food #}
    {% case 2 %}
        {# course level #}
    {% case 3 %}
        {# one dish #}
{% endswitch %}


This give you a lot of fine control over each level of your structure.

Or even simpler:

{% set entries = craft.entries.section('food').descendantOf( entry ) %}


and run the same loop regardless of which level you are on.

You can also have a look at this page to see how to create a navigation for a structured section.

And if you want elaborately styled menus check out this link