"Eu como tomate."
This should be translated to "I eat a tomato" or something. In English we wouldn't put "tomato" without an article.
I think that for habitual actions, Americans would say 'I eat tomatoes' rather than 'I eat tomato'.
A more natural translation would be "I eat tomatoes" or "I eat a tomato." The translation given "I eat tomato"X sounds unnatural.
I am really curious where the English translations come from for these sentences—because all this is a word-for-word translation of the Portuguese...
a tomato --- is correct; I think your English is not idiomatic enough AND you lose hearts if you make a mistake which is actually your mistake !!!!