Season the steak. Place the hanger steaks in a bowl or pan. Add the salt, garlic powder, black pepper, Mexican chili powder, onion powder, and ¼ cup canola oil. Toss until the steaks are well coated. Let sit at room temperature for 1 hour.
Roast the garlic and shallot. Place the garlic and shallot on aluminum foil with a little canola oil and salt. Wrap and roast at 375°F for 20–25 minutes.
Make the steak sauce. Combine the mayonnaise, hot sauce, white vinegar, thyme, roasted garlic, and roasted shallot. Mix until smooth and refrigerate until needed.
Cook the mushrooms. Heat a cast-iron skillet over medium heat. Add about 1 tablespoon canola oil and 1 tablespoon butter. Add the mushrooms and cook for 12–15 minutes, until softened and browned.
Cook the onions. Place the sliced onions on a hot griddle or plancha with a little oil and butter. Cook for 6–8 minutes, then flip and continue cooking until tender and caramelized.
Grill the steaks. Preheat the grill for direct grilling. Cook the hanger steaks for 4 minutes, flip, and cook another 4 minutes. Remove when they reach about 128°F internally.
Rest. Let the steaks rest for 10 minutes before slicing.
Toast the buns. While the steak rests, lightly toast the ciabatta buns. Spread the homemade steak sauce over the buns.
Slice the steak. Thinly slice the hanger steak against the grain.
Assemble. Pile the sliced steak onto the sauced ciabatta buns. Top with the cooked onions, mushrooms, and Mexican queso cheese. Broil or use a kitchen torch to melt the cheese before serving.