Prepare the marinade
Finely chop the garlic, thyme leaves, and rosemary leaves. Combine them in a bowl with the chilli flakes, olive oil, soy sauce, and balsamic vinegar. Mix well.
Marinate the beef
Cut the beef into large bite-sized cubes. Place them in a bowl or resealable bag and pour over the marinade. Mix well to coat, then refrigerate for 1–3 hours.
Prepare the vegetables
Slice the onion and courgette into medium-thick rounds and cut the peppers into chunks.
Assemble the skewers
Thread the marinated beef onto skewers, alternating with the vegetables and cherry tomatoes. Sprinkle lightly with salt before grilling.
Preheat the grill
Preheat the grill to 250°C. If using a rotisserie setup, place the skewers on the rotisserie attachment and start the motor.
Grill the skewers
Cook indirectly for 15–20 minutes, turning if necessary. For best results, use a meat thermometer—the internal temperature of the beef should reach at least 60°C.
If you don’t have a rotisserie, place the skewers on a rack or grill shelf and turn them regularly for even cooking.