Place a chicken breast inside a zip-top bag or between two pieces of plastic wrap. Using a meat mallet or a heavy pan, pound the chicken to an even thickness of about 1/2 inch (1.25 cm). Repeat with the remaining breasts.
In a medium bowl or shallow dish, whisk together the olive oil, lemon juice, chopped cilantro, garlic powder, salt, pepper, and red pepper flakes to create the marinade.
Add the pounded chicken breasts to the marinade, turning to coat them completely. Let the chicken marinate for at least 15 minutes at room temperature, or up to 4 hours in the refrigerator.
Place a grill pan over medium-high heat. Let it get hot for a few minutes. Brush the pan with the high-smoke-point oil.
Remove the chicken from the marinade, letting any excess drip off. Place the chicken on the hot grill pan.
Cook for 5-6 minutes on the first side without moving it, until deep grill marks appear.
Flip the chicken and cook for another 5-6 minutes on the other side. The chicken is done when it is opaque all the way through and a meat thermometer inserted into the thickest part registers 165°F (74°C).
Transfer the chicken to a cutting board and let it rest for 5-10 minutes. This allows the juices to redistribute throughout the meat.
Slice the chicken against the grain and serve, garnished with additional fresh cilantro if you like.