Add olive oil, lemon juice, garlic, ground coriander, ground cumin, sweet paprika, chili powder, salt, and black pepper to a food processor. Pulse 5–7 times to mince the garlic and begin combining the spices.
Add the parsley and cilantro to the processor and pulse a few more times until the herbs are chopped but not pureed; the marinade should be chunky rather than completely smooth.
Slice each chicken breast in half lengthwise to create 8 thinner pieces, then transfer the chicken to a large zip-top bag or bowl.
Pour the herb-spice marinade over the chicken, seal the bag (or cover the bowl) and gently massage to coat all pieces evenly.
Marinate in the refrigerator for at least 4 hours or overnight for best flavor.
Preheat a grill or grill pan to medium heat. Grill the chicken pieces until cooked through and no longer pink in the center, about 3–6 minutes per side depending on thickness.
Remove from the grill and let rest a few minutes before serving.