You can, but it is an errand rather than a download. Travellers describe going into an Ethio Telecom branch in person to have one issued, taking the ID they registered with, and finding that not every branch keeps eSIMs in stock. One traveller was pointed to a specific store because it was the one that reliably had them.
The people who get caught out hardest are those arriving with an eSIM only iPhone. A US iPhone 14 or later has no SIM tray at all, so there is no physical card to fall back on. If the branch you reach has no eSIM stock that day, you have no way to get online.
Buying before you fly removes the whole problem. You scan a QR code at home, land at Bole airport already connected, and never queue at a counter. 1 GB over 7 days is $5.17.