In a small bowl, whisk together the oregano, brown sugar, salt, chili powder, cumin, and garlic powder. Rub the spice mix all over the chuck roast.
Set the Instant Pot to Sauté and add oil. Sear all sides of the chuck roast until golden, about 2 minutes per side. Pour in the lager then scatter the onions over the chuck roast and secure the lid.
Set the Instant Pot to Pressure Cook/Manual on High for 55 minutes. When done, let the pressure release naturally for 10 minutes, then follow the manufacturer’s guide for quick release, making sure to wait until the cycle is complete before unlocking and removing the lid.
Preheat oven to 375°F / 190°C and line a large baking sheet with aluminum foil.
Remove the roast and use two forks to shred it into bite-size pieces.
Spread an even layer of chips onto the baking sheet, then top with one-third of the cheese, jalapeños, and shredded beef. Repeat twice more. Bake until the cheese is melty, about 10 minutes.
Garnish with avocado, radishes, cilantro, and red onion. Serve with lime wedges.