Use a paper towel to pat dry the chicken breasts. If your chicken breasts are very thick, butterfly them into smaller pieces. Season both sides of the chicken with salt, pepper, and garlic powder.
Cook the chicken:
Heat a large pan over medium-high heat. Once hot, heat the oil (or melt the butter). Place the chicken breasts on the pan and cook the first side for 5 minutes without moving them.
Flip and cook the other side for another 4 to 6 minutes until the internal temperature at the thickest part reaches 165F. Butterflied chicken breasts will take less time than thicker whole pieces, 4 minutes per side vs 6 to 8 -depending on thickness. Remove the chicken breasts from the pan onto a plate.
Make the chimichurri:
While the chicken cooks place the garlic in a food processor, and pulse several times until chopped. Add the Italian parsley (thin stems are fine), and pulse again. Add the oil, lemon juice, cumin, and salt. Pulse until combined.
Transfer the chimichurri to an airtight container or glass jar and refrigerate for up to one week.
Serve:
Serve the chicken breasts topped with chimichurri sauce over the top.