Divide the 1 lb ground beef into two 8-oz portions. Gently form each portion into a patty about 3/4 to 1 inch thick, making a slight indentation in the center with your thumb to help prevent doming while cooking. Handle the meat loosely — do not overwork.

Season patties

Sprinkle each side of the patties evenly with 3/4 tablespoon Cajun seasoning, then divide the kosher salt and black pepper between both sides (about 1/2 teaspoon salt and 1/4 teaspoon pepper per patty). Press seasoning lightly into the meat.

Preheat grill or pan

Preheat a grill or heavy skillet (cast-iron preferred) over medium-high heat until very hot. Brush the cooking surface or patties lightly with 1 teaspoon neutral oil to prevent sticking.

Cook patties

Place patties on the hot grill or skillet. For medium-rare to medium, cook about 3.5–4 minutes per side for 1-inch thick patties (internal temperature 130–140°F / 54–60°C for medium-rare to medium). Adjust time for desired doneness. Avoid pressing the patties while cooking.

Add cheese

About 1 minute before the patties are done, top each patty with two slices of pepper jack cheese. If using a skillet, reduce heat to medium-low and cover briefly or tent with foil to melt the cheese.

Onions & Toppings

Prepare onions

While the patties rest, slice the Maui onion into 1/4-inch rings or half-rings, separating into strips as you prefer.

Caramelize/grill onions

Heat a skillet or plancha over medium heat and add 1 tablespoon unsalted butter and 1 teaspoon olive oil. When the butter foams, add the sliced onions and a pinch (about 1/8 tsp) of salt. Cook, stirring occasionally, until softened and golden, about 8–12 minutes. If the onions begin to brown too fast, add 1–2 tablespoons water to deglaze and steam them gently until tender. Toward the end, sprinkle an additional 1/2 teaspoon Cajun seasoning over the onions and toss to incorporate for a spicy finish.

Toast buns

Butter the cut sides of the burger buns with the reserved 1 tablespoon unsalted butter. Toast them on the grill or in a skillet, cut-side down, until golden and crisp, about 1–2 minutes.

Spicy Cajun Aioli

Make aioli

In a small bowl, whisk together 1/2 cup mayonnaise, 1 teaspoon Cajun seasoning, 1 teaspoon hot sauce, 1 teaspoon fresh lemon juice, 1 minced garlic clove, 1/4 teaspoon smoked paprika (if using), 1/8 teaspoon black pepper, and 1/8 teaspoon salt until smooth. Taste and adjust seasoning or hot sauce level to preference. Chill briefly if time permits to let flavors meld.

Assembly & Serve

Spread about 1–1 1/2 tablespoons of the spicy Cajun aioli on the bottom half of each toasted bun.

Place a lettuce leaf (if using) on the aioli, then set the hot, cheese-topped patty on top.

Top each patty with a generous portion (about 1/4 cup) of the grilled Maui onions, then add tomato slices and pickles as desired.

Spread a light smear (about 1 teaspoon) of aioli on the top bun, close the burger, and serve immediately.

Optional: Serve with fries or a side salad and extra aioli for dipping.