Blend the chimichurri sauce by adding fresh parsley, garlic, red wine vinegar, olive oil, red pepper flakes, kosher salt, and black pepper into a food processor. Pulse until you achieve a chunky texture, and set aside.

Marinate the sirloin steak cubes by placing them in a bowl with half of the prepared chimichurri sauce. Give them a gentle toss, and let them marinate for at least 30 minutes.

Soak the bamboo skewers in water for about 30 minutes to prevent burning.

Thread the marinated steak cubes onto the soaked skewers, adding optional vegetables if desired.

Preheat your grill to medium-high heat, around 400°F (200°C). Lightly oil the grates.

Grill the skewers for approximately 8-10 minutes, turning them occasionally until the steak reaches your desired level of doneness.

Drizzle the remaining chimichurri sauce over the skewers right before serving.