Up to current versions of Cloud Composer (1.9.0 at the time of writing), the gcloud composer environments run command works by connecting to the Kubernetes master of your environment's GKE cluster. The error means there is something is potentially wrong with the configuration given to you by the GKE API, or there is something intercepting your traffic (like a non-transparent proxy on a corporate network). You should verify that you can connect to the Kubernetes master using kubectl and resolve any issues with that before trying to use the Composer command.
To connect using kubectl, obtain cluster credentials and then try issuing a few commands:
gcloud container clusters get-credentials --zone=$Z $COMPOSER_CLUSTER_NAME
kubectl get pods
To answer your question directly, you can use --insecure-skip-tls-verify can fix your issue if you use kubectl, but this option cannot be passed to gcloud composer.