Instructions

• Rinse the onion in a fine-mesh strainer under cold water and let the excess water drain off. In a medium bowl mash the avocado and mayonnaise together with a fork. Stir in the onion, tomatoes, cilantro, lime juice and garlic. Season generously with salt. Cover with plastic wrap, pressing the wrap directly onto the surface, and set aside. (The mayonnaise can be prepared up to 8 hours ahead.)

  Related Grill Skills

  Dicing an Avocado

  Mincing Garlic
• Prepare the grill for direct cooking over high heat (230°C to 290°C).
• Brush the cooking grates clean. Grill the poblano chile peppers over direct high heat, with the lid closed, until the skin is blackened on all sides, about 10 minutes, turning occasionally. Transfer the chile peppers to a bowl and cover with plastic wrap to trap the steam. Let stand for about 10 minutes. Remove the chile peppers from the bowl and peel off and discard the blackened skin, stems and seeds. Chop the chile peppers into 1 centimetre dice.
  Brush the cooking grates clean. Grill the poblano chile peppers over high heat, with the lid closed, until the skin is blackened on all sides, about 10 minutes, turning occasionally. Transfer the chile peppers to a bowl and cover with plastic wrap to trap the steam. Let stand for about 10 minutes. Remove the chile peppers from the bowl and peel off and discard the blackened skin, stems and seeds. Chop the chile peppers into 1 centimetre dice.
• Mix the ground chuck, chile peppers, 1½ teaspoons of salt and the pepper; then shape into four patties of equal size, each about 2 centimetres thick. With your thumb or the back of a spoon, make a shallow indentation about 2.5 centimetres) wide in the centre of the patties to keep them from forming a dome as they cook.
• Grill the patties over direct high heat, with the lid closed, until cooked to medium doneness, 8 to 10 minutes, turning once when the patties release easily from the grate without sticking. During the last minute of cooking time, toast the buns, cut-side down, over direct heat. Build each burger on a bun with a patty and a dollop of the guacamole mayonnaise. Serve warm.
  Grill the patties over high heat, with the lid closed, until cooked to medium doneness, 8 to 10 minutes, turning once when the patties release easily from the grate without sticking. During the last minute of cooking time, toast the buns, cut-side down, over direct heat. Build each burger on a bun with a patty and a dollop of the guacamole mayonnaise. Serve warm.