event.rb

class Event < ApplicationRecord
  # Associations
  belongs_to :owner, class_name: "User", optional: true
  belongs_to :event_source, polymorphic: true

  has_noticed_notifications

  # ...
end

event_notification.rb

class EventNotification < ApplicationNotification
  deliver_by :action_cable, format: :to_websocket, channel: "NotificationChannel"
  deliver_by :email, mailer: "NotificationsMailer", method: :notify #, delay: 15.minutes, unless: :read?

  param :event

  def message
    "#{event.event_source}: #{event.title}"
  end

  def url
    target = [event.event_source.parent, event.event_source].compact

    polymorphic_path(target.one? ? target.first : target)
  end

  def event
    params[:event]
  end
end

notifications_mailer.rb

class NotificationsMailer < ApplicationMailer
  def notify
    @record = params[:record]
    @recipient = params[:recipient]

    # I'd like to get access to the Noticed::Base here
    @message = @record.message

    mail(
      to: email_address_with_name(@recipient.email, @recipient.name),
      from: Jumpstart.config.support_email,
      subject: "Reactive Rails Reviews - Notification"
    )
  end
end