I don't think English and Hebrew are the same in this situation. Compare "עגבניות זה בריא", a legitimate sentence, with "tomatoes is healthy". In Hebrew "זה" is used for this kind of general statements - "ספרים זה סטימצקי", or "צעצועים זה אנחנו", or "מים זה כל מה שאני צריך" (all of which are plural), "אכילה מרובה זה מה שגורם להשמנה" (feminine) etc.
So in this case, in the Hebrew sentence, there's no need to infer anything - the meaning is simply that "tomatoes are healthy". In the suggested English translation, either you infer "eating" or you understand incorrectly that "buying tomatoes is healthy". But either way, "Buy tomatoes, they are healthy." is the best translation in my view.
The first clause and the second clause are connected by "it". So "buying tomatoes, it is healthy" connects "it" to "buying". And "buy tomatoes, they are healthy" connects "they" to "tomatoes". But "buy tomatoes, it is healthy" leaves unclear what "it" refers to, so it is a poorly constructed sentence. This is an example of a dangling participle.