Hello, @ebanster!
Thank you for your question!
There’s no native option for what you are looking to do, but a workaround you can try is to have a separate step on the pipeline in question with a script that talks to the GitLab API.
This way, you can trigger a pipeline on GitLab’s side. Note that in this case, Buildkite will have no way of knowing if that pipeline failed or succeeded on GitLab’s side.
Cheers!