Step 1

Working with one chicken breast at a time, place the chicken between 2 pieces of plastic wrap or parchment paper. Gently pound with a meat mallet to 1/2 inch thick then transfer to a large bowl.

Step 2

Combine the yogurt, lemon zest, lemon juice, scallion whites, garlic, olive oil, 2 teaspoons salt and a few grinds of black pepper to a food processor and process until smooth. Pour the marinade over the chicken. Turn the chicken a few times to coat then submerge in the marinade. Cover the bowl with a clean dish towel and refrigerate for at least 30 minutes but no more than 3 hours.

Step 3

Meanwhile, heat a grill to medium.

Step 4

Remove the chicken from the marinade to a large platter, letting any excess marinade drip back into the bowl. Season the chicken with 1/2 teaspoon salt and a few grinds of black pepper. Grill, covered, flipping once halfway through, until a digital thermometer registers 165 degrees F, 4 to 5 minutes per side. Let rest 5 minutes before serving.

Step 5

Thinly slice the scallion greens on a bias and sprinkle over the chicken. Refrigerate in an airtight container for up to 5 days.