Make chimichurri sauce: Add parsley, cilantro, oregano, and garlic to a food processor. Pulse until finely chopped. Add apple cider vinegar and pulse again. With the motor running, drizzle in olive oil until combined. Stir in salt, pepper, and crushed red pepper flakes. Adjust seasoning as desired.

Marinate chicken: Place chicken thighs in a shallow dish. Pour ¼ cup chimichurri over the chicken and toss to coat evenly. Cover and refrigerate at least 30 minutes or overnight for stronger flavor.

Make couscous salad: In a large bowl, toss cooked couscous with ¼ cup chimichurri sauce. Add halved tomatoes, feta, and chives. Season lightly with salt and pepper. Toss and set aside to let flavors develop.

Grill chicken: Preheat grill or grill pan over high heat for 10–15 minutes. Grill chicken 5 minutes per side or until cooked through and internal temperature reaches 165°F (75°C).

Rest & serve: Let chicken rest 5 minutes. Serve with couscous salad and extra chimichurri drizzled on top for added flavor.