- ¼ cup + 2 Tablespoons vegetable oil, divided
- 3 cloves garlic, halved
- 2 small serrano chile peppers or 1 small jalapeno chile pepper, halved
- ½ cup loosely packed cilantro
- ⅓ cup freshly squeezed lime juice (about 2 limes)
- 1 teaspoon salt
- ¼ teaspoon freshly ground black pepper
- 4 boneless, skinless chicken breast halves (about 1¼ pounds)
- 1 large white onion, sliced ¼-inch thick
- 2 ripe Hass avocados
- 12 corn tortillas (6" diameter)
- Heat ¼ cup of oil in small skillet over medium heat. Add garlic and chile peppers and cook, stirring frequently, until just brown, 1 to 2 minutes. Process with cilantro, lime juice, 1/2 teaspoon of the salt, and black pepper in blender or food processor until smooth.
- Put chicken in shallow dish and spread half the garlic mixture over all sides of chicken.
- Heat 1 tablespoon oil in large skillet over medium-high heat. Add onion and cook, stirring occasionally, until golden but still slightly crunchy, about 5 minutes. Chop enough of the onion to make 1/4 cup and set aside. Put rest of onion on a plate. Save the skillet.
- Peel and pit avocados and put flesh in a bowl. Add reserved chopped onion, remaining garlic mixture, and 1/4 teaspoon of the salt. Coarsely mash with potato masher or fork.
- Return skillet to medium heat and add remaining tablespoon oil. Lift each breast and let excess marinade drip off. Discard extra marinade. Add chicken to hot pan and sprinkle with remaining 1/4 teaspoon salt. Brown on one side, about 5 minutes, then flip and finish cooking, 3 or 4 minutes longer. Remove to cutting board. Put reserved sliced onion in the skillet to reheat. Scrape up any brown bits stuck to the bottom of the pan.
- Wrap tortillas in damp paper towels and microwave on high 1 minute. Remove paper towels and keep tortillas warm. Cut chicken across the grain into 1/4" slices and toss with onion in pan. Serve with tortillas and guacamole.