npm install --save parse-server-onesignal-push-adapter

var OneSignalPushAdapter = require('parse-server-onesignal-push-adapter');
var oneSignalPushAdapter = new OneSignalPushAdapter({
  oneSignalAppId:"your-one-signal-app-id",
  oneSignalApiKey:"your-one-signal-api-key"
});

var api = new ParseServer({
  push: {
    adapter: oneSignalPushAdapter
  },
  ...otherOptions
});