777-200 / 777-300 you will definitely get a lie flat. 787-9 are all lie flat. 787-8 aircraft are a mix of lie flat & slightly angled, depending on the aircraft.
See the wiki here:
Ethiopian Best Business Class Seats?
Note that ET frequently will swap equipment - so no guarantee which equipment you will get (though some routes have more frequent subs than others).
Which route are you looking at?