"I could eat more."
Translation:Θα μπορούσα να τρώω περισσότερο.
μπόρεσα=simple past, μπορούσα=past continuous. Only Θα + past continuous confers the subjective (would + verb)
The English sentence could be a simple past, though, since "could" has two meanings. "Yesterday I could eat more, but today I have a stomach ache."
The English sentence could, but the Greek translation couldn't. . To put this simpler, μπόρεσα : was able to, μπορούσα : could. If your sentence can't use "was able to" instead of could, then you need continuous. Hope that helps!
I had it as an English to Greek. Fortunately, I didn't know the past tense of the verb, so got it right.