Step 1

Finely grate the zest of 2 medium lemons into a large bowl (about 2 tablespoons). Juice the lemons until you have 5 tablespoons. Add 2 tablespoons juice to the large bowl and reserve the remaining in a medium bowl for the sauce.

Step 2

Add 1/3 cup plain Greek yogurt, 2 tablespoons of the extra-virgin olive oil, 1 tablespoon smoked paprika, and 1 1/2 teaspoons kosher salt to the large bowl and whisk until smooth.

Step 3

Prepare 1 1/2 pounds boneless, skinless chicken breasts: Working with 1 chicken breast at a time, place between 2 large sheets of plastic wrap. Using the flat side of a meat mallet or rolling pin, pound the chicken until it is about 1/2-inch thick. Transfer to the bowl with the marinade, flipping the chicken to make sure it is evenly coated. Cover and refrigerate for at least 4 hours or up to overnight.

Step 4

Let the chicken sit at room temperature for 30 minutes before cooking. Meanwhile, heat an outdoor grill for direct, medium-high heat and prepare the sauce.

Step 5

Heat a small skillet over medium-high heat. Add 1 teaspoon coriander seeds and 1 teaspoon cumin seeds. Toast, stirring frequently, until the coriander seeds turn a shade darker and smell fragrant, 30 to 45 seconds. Transfer to a food processor fitted with the blade attachment.

Step 6

Prepare the following, adding each to the food processor as it is completed: Peel and coarsely chop 2 garlic cloves. Trim and coarsely chop 1 to 2 serrano peppers. Add the remaining 3/4 teaspoon kosher salt and pulse until finely chopped, 5 to 8 (1-second) pulses.

Step 7

Coarsely chop 1/2 medium bunch fresh parsley until you have about 1 cup. Pick the leaves from 1 bunch fresh mint until you have 1 cup, then coarsely chop. Add both to the food processor and pulse until finely chopped, 8 to 12 (1-second) pulses. Add 1/3 cup roasted, shelled pistachios and pulse until coarsely chopped, 5 to 8 (1-second) pulses.

Step 8

Transfer to the bowl with the reserved lemon juice. Add the remaining 1/3 cup extra-virgin olive oil and stir to combine. Taste and season with more kosher salt as needed. Cover with plastic wrap, pressing the wrap directly onto the surface of the sauce.

Step 9

Scrape the grill grates clean if needed. Lightly oil the grill grates with neutral oil. Place the chicken on the grill. Grill uncovered until the thickest part of the chicken registers an internal temperature of 155 to 160°F (it will get up to 165°F when it is resting), 3 to 5 minutes per side. (If you want criss-cross grill marks, rotate the chicken 45 degrees on the same side after 1 1/2 to 2 minutes.)

Step 10

Transfer the chicken to a plate, tent with aluminum foil, and let rest for 5 to 10 minutes. Meanwhile, halve, seed, and peel 1 large ripe avocado. Cut into 1/2-inch chunks, add to the sauce, and gently fold until the avocado is fully coated.

Step 11

To serve, cut the chicken across the grain into 3/4-inch thick slices and arrange on a serving platter. Spoon the avocado-pistachio sauce over the chicken. Serve immediately or at room temperature.