Chop the fresh herbs very finely. Combine the chopped cilantro, parsley, and basil together in a small bowl. Add olive oil, red wine vinegar, minced garlic, and serrano pepper. Season with sea salt and freshly cracked pepper, to taste. Set aside to allow flavors to mingle.
Cut the chicken breasts into same sized bite sized pieces. Whisk the marinade and pour half into a bowl. Cover and set aside on the counter for later use.
Place the chicken in the other bowl with half of the chimichurri sauce. Stir to coat evenly. Cover and refrigerate for 1 hour.
Remove from the refrigerator and skewer the chicken pieces alternating with the red onion and grape tomatoes. Discard the chicken marinade. Season the skewers with sea salt and freshly cracked pepper, to taste.
Heat a grill pan over medium high heat. Spray the grill pan with cooking spray then add the chicken skewers to the pan, making sure not to overcrowd. Turn the skewers every 3-4 minutes, for a total of about 9-10 minutes or until the chicken is cooked through.
Place the chicken on a serving plate and serve with the reserved marinade. Enjoy.