Rub the roast with the salt and set aside.
Combine the garlic, onion, and chile in a medium-sized bowl. Stir in the sugar, beer, orange juice and zest, lime juice, cilantro, 2 tablespoons olive oil, and a pinch of salt. Blend the mixture together using an immersion blender. Taste and adjust seasoning.
Place the roast in a shallow bowl or baking dish and cover with the orange juice mixture. Marinate for at least an hour or overnight.
Remove meat from the fridge at least 30 minutes before grilling. Light the grill (if using charcoal, wait until the coals are glowing and ashy on top; if using gas, preheat to high on one side and medium-low on the other). Pat the meat dry and place over the hot coals, fat side down. Sear for 2 minutes, then flip and sear again.
Move the steak over to the edge of the coals or cooler side of the grill, close the lid and adjust the vents to keep the grill at around 350°F, and cook for an additional 20-30 minutes, or until a meat thermometer reaches 120°F (the timing will vary depending on the thickness of the roast, so make sure you have a meat thermometer you trust).
While the steak is cooking, heat a skillet over the center of the coals and add 1 tablespoon olive oil. When that shimmers, add the peppers, onions, and a pinch of salt and cook, stirring occasionally until the peppers and onions have softened, blackened a bit at the edges, and cooked down, 15 to 20 minutes.
Remove the roast from heat, transfer to a cutting board, and cover with foil. Rest 15 to 20 minutes, then thinly slice and transfer to a platter. Stir a squeeze of lime into the peppers and onions.
Serve alongside the steak with warm flour tortillas, sliced avocado, and lime wedges.