Can I access rails app resources from Rails Engine or Mountable Engine?

I want to create a gem that is Rails Engine (or Mountable Engine). And it wants to list resouces from parent rails app.

For example:

# one rails app on routes
mount MyGem::Engine, at: '/my_gem' if Rails.env.development?

And when I access /my_gem, I want to list files from app/views/foo/xxxx, app/assets/my_gem/xxxx etc (not my gem views, assets).