Cilantro-Lime Grilled Chicken Tacos

1 Mix the salsa, 2 tablespoons of the lime juice, cilantro, oil, cumin and salt in a bowl or shallow baking dish. Add the chicken and toss the pieces to coat. Set aside to marinate 15 – 20 minutes while you prepare the other ingredients, or cover and refrigerate up to 3 hours.
2 Scoop the avocado flesh into a bowl and add the remaining 2 tablespoons lime juice and ½ teaspoon salt. Lightly mash with a potato masher or wooden spoon. Taste for seasoning and add more lime juice or salt.
3 Heat an outdoor grill to medium-high or an oiled heavy grill pan or cast-iron skillet indoors on the stovetop (be sure to use your exhaust fan or open a window). Cook the chicken, turning frequently until cooked through, about 7 minutes per side. Let the chicken rest 10 minutes, then slice or chop into bite-size pieces.
4 To make the tacos, put some lettuce leaves on each tortilla. Put a spoonful of mashed avocado on the lettuce. Arrange the chicken on top. Top with cheese, more salsa and additional garnishes, if desired.