Mince the 3 garlic cloves finely and set aside. Dice the onion into small pieces (about 3 tablespoons worth). Seed the tomatoes and dice them into 1/4-inch pieces—this removes excess moisture so your guacamole doesn't get watery. Slice the green chili into thin rings, removing seeds if you prefer less heat. Roughly chop the coriander (cilantro). Have all ingredients prepped and within arm's reach before you start making the guacamole.

Spread the butter evenly on both sides of all 4 bread slices. Heat a skillet over medium-high heat or preheat an air fryer to 400°F. Toast the bread for 3-4 minutes until golden and crispy with a slight crunch—this gives the sandwich structural integrity so it won't get soggy from the guacamole. Set the toasted bread aside on a clean surface.

Cut the avocado in half lengthwise, remove the pit, and scoop the flesh into a bowl. Mash it with a fork until you reach your desired consistency—I prefer leaving it slightly chunky for texture rather than completely smooth. Pour in the freshly squeezed lemon juice immediately and gently fold it in; the acid prevents browning and adds brightness. Add the minced garlic, diced onion, tomato pieces, green chili, salt, pepper, cumin, and chopped coriander from Step 1. Fold everything together gently until just combined, being careful not to overmix or the guacamole will become mushy.

Lay out 2 slices of the toasted bread from Step 2. Place a lettuce leaf on each slice for a moisture barrier—this keeps the bread from getting soggy. Spread half of the guacamole mixture from Step 3 onto each lettuce-lined slice. Drizzle lightly with the extra virgin olive oil for a silky finish and added richness. Top each sandwich with the remaining 2 slices of toasted bread. Serve immediately while the bread is still warm and crispy.