Yes, some (probably older) Mizrahim still pronounce ע in a different from א - but most of the speakers pronounce it in the same way. However - yes, there is a difference between the עו in עוגה and the או in אוכל. (please, Hebrew, don't mess up the languages) עוגה is pronounced /oogah/, and אוכל is pronounced /okhel/. This is because that vav can make a /v/ sound, and /u/ sound or an /o/ sound.
Aside from the topic of Hebrew, I'd just like to point out that, as a native English speaker (and teacher), the below -- Translation: I eat a cake.
-- is not correct English. If I were teaching an ESL student, I'd correct him or her. As with chicken, we don't count "cake". Because who eats a whole cake (or chicken) in one sitting?
In English we say "I'm eating cake (right now)" or "I eat cake (every night)" (as a repetitve action).
The only situation I could think of with the indefinite pronoun is something on the order of, "I am so hungry I could eat a (whole) cake."
On the other hand, one could say "I am eating a cupcake," or "I eat a cupcake (for breakfast every morning." But not a cake!