In a medium bowl combine the ground beef, kosher salt, black pepper and garlic powder. Mix gently with your hands or a fork until just combined — avoid overworking. Divide into 2 equal portions (for larger single patties) or 4 smaller patties, then form into patties about 3/4 inch thick. Make a shallow dimple in the center of each patty with your thumb to reduce puffing while cooking.

Cook patties

Heat a cast-iron skillet or heavy frying pan over medium-high heat and add the olive oil. When shimmering, add patties (do not overcrowd). Cook for 3-4 minutes on the first side without moving to develop a sear. Flip and cook 2-3 minutes more for medium (adjust time for desired doneness). If using cheese, place a slice of pepper jack on each patty during the last minute of cooking and cover the pan to melt. Remove patties to a plate and rest for 3 minutes.

Guacamole

Prepare avocados

While the patties rest, halve and pit the avocados. Scoop flesh into a bowl and mash with a fork, leaving some small chunks for texture.

Season guac

Add lime juice, minced red onion, minced jalapeño, chopped cilantro, salt, black pepper and diced tomato (if using). Stir gently to combine. Taste and adjust salt or lime as needed. Keep covered or at room temperature until assembly to avoid browning.

Toppings & Assembly

Toast buns

Spread butter on cut sides of the burger buns. Toast buttered sides face-down in a dry skillet over medium heat 1-2 minutes until golden and crisp. Remove and set aside.

Prepare sauce

Mix mayonnaise and hot sauce (if using) in a small bowl. Adjust heat to taste.

Assemble burgers

Spread about 1-2 tablespoons of the mayo sauce on the bottom bun. Place a lettuce leaf, then the warm cheeseburger patty. Spoon 3-4 tablespoons of guacamole onto the patty (or more to taste) and top with tomato slice and a ring or two of red onion. Spread a little mayo on the top bun and close the burger. Repeat for remaining burgers. Serve immediately.