The Mandalorian has referenced the Star Wars prequels; in the previous episode, "The Gunslinger", Mando lands on Tatooine and is immediately greeted by a trio of DUM-series pit droids. But referencing Gungans is easily one of the series' most overt callouts.
Jar Jar Binks was one of the main characters in Jar Jar Binks actor Ahmed Best received while the prequels were still in theaters and in the years since. And now, with The Mandalorian, it seems that the joke about Gungans being ridiculed in the galaxy is still alive.
On the way to the prison transport in The Mandalorian episode 6, "The Prisoner", Bill Burr's Mayfield makes fun of Mando's refusal to remove his helmet. He wonders if Mando is a Gungan underneath the armor and subsequently asks, "Is that why youssa don't want to show your face?" It's played off as a joke, but beyond that, it's one of the biggest references yet to the prequel trilogy - and the first reference to Jar Jar Binks and the Gungans in the series.
What's more interesting is that Mayfield knows what Gungans are. They aren't typically well-known outside of Naboo. Even Qui-Gon and Obi-Wan weren't sure what Jar Jar Binks was when they first met him. But considering that Jar Jar Binks played an integral role in bestowing emergency powers to Supreme Chancellor Palpatine when the Galactic Republic was still around - and then later paid the price for his mistake by ultimately becoming a street performer on the planet Theed and being ridiculed by those old enough to know what he did - it's possible that Mayfield knows of Gungans because of Jar Jar Binks. As mentioned earlier in the episode, Mayfield was an Imperial sharpshooter.
Regardless of how well-known Gungans are and how Mayfield knows about them, the moment is arguably one of the best references The Mandalorian has had yet. It's become a show that's quite self-aware of the Star Wars galaxy, making more and more meta references with each ing week. Last episode saw a major reference to Han Solo and now there's been one for Jar Jar Binks, delivered by Burr, who is a comedian nevertheless. We'll just have to wait and see if there are any more big references as The Mandalorian heads into its season finale.