RxJS alternative to doing a Promise.resolve?

Observable.of is what you are looking for (see this plunk):

// You might need to add this import in RxJS versions earlier than 5
import 'rxjs/add/observable/fromArray';

// ... or this line in RxJS 5+
import 'rxjs/add/observable/of';

if (me.groups) {
  return Observable.of(me.groups);
}