So, for reference, I can say from everyday experience that Debian now ships with a UEFI stub compiled into its kernel, enabling the kernel to be directly booted without any middleman by your firmware, assuming it is a competent EFI-compliant firmware. This is not esoteric knowledge, though neither is it a default. Anyway, unsurprisingly, it looks like this ability is inherited and perfectly usable by Ubuntu, e.g.: How to boot load the kernel using EFI stub (efistub) loader?