Divide the ground beef into two equal portions (about 8 oz each). Gently form each portion into a patty about 3/4 inch thick and 4 inches in diameter. Make a shallow indentation in the center of each patty with your thumb to reduce puffing while cooking. Do not overwork the meat.

Season

Season both sides of each patty evenly with kosher salt, black pepper, garlic powder, and onion powder.

Cook Patties

Heat a heavy skillet or cast-iron pan over medium-high heat until very hot. Add 1 tablespoon oil and swirl to coat. Place patties in the pan and cook undisturbed for 3-4 minutes until a brown crust forms. Flip and cook 2-3 minutes on the second side for medium (adjust time for desired doneness). In the last 60 seconds of cooking, place a slice of pepper jack cheese on each patty, cover the pan briefly or tent with foil to melt the cheese.

Rest

Remove patties from the pan and let rest on a plate for 3 minutes to redistribute juices.

Guacamole (California-style)

Prepare Avocados: Halve the avocados, remove pits, and scoop flesh into a medium bowl.

Mash & Mix: Add lime juice and mash the avocados to a slightly chunky consistency with a fork. Fold in the minced red onion, chopped cilantro, minced jalapeño, diced tomato, kosher salt, and black pepper. Taste and adjust seasoning or lime if needed. Keep chilled until assembly.

Assembly & Toppings

Toast Buns: Butter the cut sides of the buns lightly. On a clean skillet or in the pan used for patties over medium heat, toast the buttered sides until golden, about 1-2 minutes.

Build the Baja Burger: Spread burger sauce or mayo on the bottom bun if using. Place a handful of shredded lettuce on the bun, then the cheese-topped beef patty. Spoon 2-3 tablespoons of the guacamole over the hot patty. Top with sliced red onion and pickled jalapeños if desired. Close with the top bun and press gently.

Serve: Serve immediately with your choice of side (fries, chips, or a simple slaw). Provide extra lime wedges and extra guacamole on the side if desired.