Step 1: Prepare the Chimichurri Sauce

1. In a small mixing bowl, combine the parsley, cilantro (if using), garlic, olive oil, red wine vinegar, red pepper flakes, salt, black pepper, and lemon juice. Stir until well combined.
2. Taste the sauce and adjust the seasoning or vinegar to suit your preference. For a spicier kick, add more red pepper flakes.
3. Cover and refrigerate for at least 30 minutes to allow the flavors to meld.

Step 2: Marinate the Chicken

1. Pat the chicken breasts dry with paper towels.
2. In a small bowl, mix olive oil, smoked paprika, garlic powder, onion powder, salt, and black pepper.
3. Rub the spice mixture evenly over both sides of the chicken breasts.
4. Place the chicken in a shallow dish or resealable plastic bag. Pour half of the chimichurri sauce over the chicken, reserving the other half for serving. Ensure the chicken is well coated, then cover and marinate in the refrigerator for 30 minutes to 2 hours.

Step 3: Cook the Chicken

Grilling Method:

1. Preheat the grill to medium-high heat and lightly oil the grates to prevent sticking.
2. Place the marinated chicken on the grill and cook for 6-7 minutes per side, or until the internal temperature reaches 165°F (74°C).

Pan-Searing Method:

1. Heat 1 tablespoon of olive oil in a large skillet over medium-high heat.
2. Add the chicken breasts and cook for 5-7 minutes per side, or until golden brown and fully cooked through.

Baking Method:

1. Preheat the oven to 400°F (200°C).
2. Place the marinated chicken in a baking dish and bake for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).

Step 4: Serve

1. Transfer the cooked chicken to a serving platter.
2. Drizzle the reserved chimichurri sauce generously over the chicken.
3. Garnish with additional chopped parsley or cilantro, if desired. Serve hot with your favorite sides.