Steak Kebabs with Chimichurri

Name: Steak Kebabs with Chimichurri
Ingredients: 1 1/4 pounds beef ((sirloin or Angus) cut into 1-inch cubes); fresh ground pepper; 1 1/4 tsp kosher salt; 1 large red onion (cut into large chunks); 18 cherry tomatoes; 6 bamboo skewers (soaked in water for 1 hour); 2 packed tbsp parsley (finely chopped (no stems)); 2 packed tbsp chopped cilantro; 2 tbsp red onion (finely chopped); 1 clove garlic (minced); 2 tbsp extra virgin olive oil; 2 tbsp apple cider vinegar; 1 tbsp water; 1/4 tsp kosher salt; 1/8 tsp fresh black pepper; 1/8 tsp crushed red pepper flakes (or more to taste)