Prepare the Chicken Skewers:
If you’re using wooden skewers, soak them in water for about 30 minutes to prevent burning.
Thread the chicken cubes onto the skewers alternating with pieces of bell peppers, red onion, and cherry tomatoes.
Season the skewers with salt and pepper, and lightly brush with olive oil.

Grill the Skewers:
Preheat your grill or grill pan over medium-high heat.
Place the skewers on the grill and cook for about 6-8 minutes per side, or until the chicken is fully cooked through and the vegetables are slightly charred. Turn occasionally for even cooking.

Make the Tomato Sauce:
While the skewers are grilling, prepare the tomato sauce.
Heat sunflower oil in a saucepan over medium heat. Add minced garlic and sauté for about 1 minute until fragrant.
Pour in the crushed tomatoes or tomato passata, add dried oregano, salt, pepper, and red pepper flakes if using.
Simmer the sauce gently for about 10-15 minutes, stirring occasionally, until it thickens slightly.

Serve:
Once the chicken skewers are done, remove them from the grill and let them rest for a few minutes.
Serve the grilled chicken skewers alongside the tomato sauce for dipping or drizzling.

Tips:
You can customize the vegetables on the skewers based on your preferences or what you have on hand.
If using wooden skewers, remember to soak them beforehand to prevent burning.
Adjust the seasoning of the tomato sauce to your taste. You can add fresh herbs like basil or parsley for extra flavor.