In a small bowl, whisk together 1/2 cup lemon juice, 1/4 cup olive oil, 1 teaspoon kosher salt, 1/2 teaspoon freshly ground black pepper, and 1 teaspoon fresh thyme (or 1/4 teaspoon dried).
Place the 2 pounds of chicken breasts in a large freezer-safe plastic bag, pour in the marinade, squeeze out excess air, and seal.
Massage the bag so the chicken is evenly coated, then place the bag in a dish and refrigerate for at least 30 minutes or up to overnight.
Preheat the grill over medium-high heat for about 5 minutes and oil the grates lightly with olive oil.
Grill the chicken over direct heat with the cover closed for about 5 minutes per side, turning once, until lightly charred.
Move the chicken to indirect heat and continue cooking 5 to 10 minutes more, until an instant-read thermometer inserted into the thickest part reaches 165°F (74°C).
Transfer the chicken to a cutting board, tent loosely with foil and rest for 10 minutes, then slice or chop as desired.