How does one turn a debootstrap rootfs into a bootable custom EFI ISO with GRUB?

I'm experimenting with creating a "custom" specific-purpose Linux distro based on Debian (Clonezilla-style, or even GPartedOS-style). In my case, it's a Python script that runs at boot. Right now, it's a simple "Hello, World!" application that refreshes the screen with how many seconds the script has been running (just as a test). I've created a script to generate a rootfs as well as compile and install Python 3.11 within it: # Boot image build script # Builds a small, specific-purpose bootable (UEFI-only) x64 ISO based on Debian. # This script currently only supports running on Debian hosts!!! set -e ROOT_DIR="rootfs" # Run debootstrap to create the rootfs if it doesn't exist [ ! -d $ROOT_DIR ] && sudo debootstrap --arch=amd64 buster $ROOT_DIR set +e # if this isn't here, any future failure will cause the script to stop, and the temporary directories won't be unmounted, which means host system will slowly break down until a reboot. # Enter CHROOT and modify rootfs cat /var/lib/dbus/machine-id apt-get install linux-image-amd64 live-boot linux-headers-amd64 grub-efi -y # apt-get install python3 apt-get clean -y EOF PYTHON_INSTALL_SCRIPT=$( cat build-python.sh ) cat build-python.sh | sudo chroot $ROOT_DIR cat << EOF | sudo chroot $ROOT_DIR # Cleanup before we leave rm /var/lib/dbus/machine-id && rm -rf /tmp/* umount /proc /sys /dev/pts EOF My goal is to turn this into a bootable UEFI-only ISO with GRUB, since this image will have tools not compatible with BIOS/CSM systems. How do I turn this into a bootable GRUB ISO image (I might want the final ISO image to have some extra files in it, so the ISO will be created from a directory.)