This hidden gem serves up vegan comfort food that'll transport you to the '50s

Even in Pawnee, Indiana, Leslie Knope and the rest of the "Parks and Recreation" crew would visit JJ’s Diner often, where Leslie would order waffles topped with whipped cream and Ron Swanson ordered a dish that came with scrambled eggs, bacon, hashbrowns, chicken fried steak, sausages, ham, pancakes and waffles.

Why are all these places such staples in these beloved sitcoms? Easy, they are diners! No one can resist good diner food, not even the Pink Ladies or the T-Birds.

There’s a comforting feeling when you bite into a juicy burger, dipping your golden, crispy fries into your chocolate milkshake, topped with whipped cream and a singular maraschino cherry.

Diner food can’t help but put a smile on your face, making you feel like you’ve stepped in a time machine and ended up on the set of "Happy Days."

Everyone should have the chance to enjoy delicious diner food and Karl Poechlauer is making that happen one fricken sandwich at a time.

Poechlauer is the man behind Substance Diner, a retro food truck that serves up vegan comfort food that’s so good you won’t even realize you're not eating meat.

About five years ago, Poechlauer, who has worked in all kinds of restaurants since he was in his 20s, decided it was time to start his own food truck. Wanting to go with a '50s aesthetic, he built his very own food truck out of a vintage camper. To go with the theme, he made sure his menu included all the diner classics you’d see at a burger joint back in the day.

“I didn't really see anybody else doing that at the time,” Poechlauer said. “It seemed like another way to differentiate it, having the retro style and the food to match that.”

As you head behind Screwbean Brewing, located at 103 N. Park Ave., you’ll see the vintage 1961 camper decorated with string lights and a red-and-white striped tarp. Neon lights cover the trailer, along with a 1950s-esque diner sign and cherry-red bar stools.

When Substance Diner first opened, Poechlauer was a vegetarian and wanted to make sure his menu had all kinds of options for everyone to enjoy. Over time, he got busier and realized the menu was a little too big.

He ultimately decided to narrow things down and focus on vegan dishes. Breakfast sandwiches, classic diner burgers with Beyond Meat patties, fried pickles, Sonoran dogs and TLTs (tofu, lettuce and tomatoes) are just a few of the tasty items found at Substance Diner.

A real standout on Poechlauer’s menu is his spicy fricken sandwich. To create his fake chicken, or fricken as he calls it, he uses seitan, a meat alternative made out of gluten. First, he makes the seitan dough and boils it in a broth.

Once the patties are boiled, it’s time to fry them. Like frying anything else, Poechlauer covers the patties in flour and breads them, using an egg replacer to make sure everything sticks together. They are then fried until golden brown.

Now it’s time to assemble the sandwich. Poechlauer toasts the buns on the flat top, then adds shredded lettuce, slices of organic tomatoes and pickles, topping it all off with vegan spicy mayonnaise.

One bite of the fricken sandwich and you won’t ever feel the need to go to Chick-Fil-A again. The seitan is perfectly crispy and mimics the texture of chicken; you truly can’t tell you're not eating meat. The crispy patty mixed with the fresh vegetables is already a top-notch combo, but it’s the spicy mayo that adds a flavorful kick, leaving your mouth buzzing.

The best part: it’s not greasy or heavy! You won’t feel weighed down after eating a fricken sandwich; it is an elevated version of a classic chicken sandwich.

You can’t have a chicken sandwich without a side of fries — it’s a crime! Thankfully, Substance Diner makes some of the best steak fries in Tucson. The thick-cut fries are the perfect combination of crispy and fluffy. You’ll never have to worry about getting thin, soggy fries here.

“As a kid, I remember Denny's or places like that, they'd always have these really big, chunky fries, and that's why I call them diner fries,” Poechlauer said.

You’ll want to leave room for dessert so you can sip on a creamy vegan milkshake or malt. Vanilla, chocolate, strawberry, chocolate peanut butter, cookies-and-cream and Coca-Cola are all on the menu. Good luck trying to choose just one.

Once you try this hidden gem, you’ll be gathering your friends and heading here all the time, just like your favorite sitcom cast.

For more information on their menu and their hours, check out Substance Diner's website.