List all products on Category page

[freakystreak]

I am using 2.3.4.I CE Frozen and I would like to show all the products that are inside all subcategories on one page when the category is selected.

Ideally i would like this the same as product_listing but be shown once the parent category link is selected. So instead of it showng (as currently) all the subcategories, it shows all the products inside those sub categories as one complete listing. Is there any way to do this? I've seen some very old add ons that will do something similar but they and over 10 years old. Has anyone done this on the newer BS version of OSC or maybe has an idea of where to start?