How do I properly access plugin controllers from the front-end?
Rather than submitting the form, try hitting it with the Craft JS object. Per the docs:

var data = {
    // ...
};

Craft.postActionRequest('cocktailRecipes/ingredients/saveIngredient', data, function(response) {
    // ...
});


https://craftcms.com/docs/plugins/controllers#posting-to-controller-actions-with-javaScript