Mingoia last week suggested his initial month-long deal was due to carry on into the new year and he will now remain at the Crown Ground for a further three months until January 18.
The midfielder, who turns 21 on Saturday, has made five appearances for the Reds and scored in the recent 3-2 defeat to Rochdale.
"I didn't know what to expect when I came here but it's been great," said Mingoia. "I've enjoyed my time here and would like to stay here as long as possible and play as many games as I can.
"At Watford, the places were very limited but here I've had a taste of first-team football and I want to get as much of it as I can."
Stanley boss Paul Cook added: "We're very pleased that Piero's staying. He's done well for us so far and hopefully he can continue to improve in the future."
