Translation:Thank you for the food we are about to receive.
You have not yet received the food - it is about to be brought to the table. So basically it is still in the kitchen…and when you translate it with "that we are receiving" it indicates that the food is in the midst being brought to you at that very moment, which isn't the case.
The sentence uses the inifinitive form of the verb "ricevere" -- to receive. So, the literal translation would generally use that form. The translation meaning "we are receiving" implies something that is happening right now. In Italian, that is generally done using the gerund form, something like "Grazie per il cibo stiamo ricevendo".