In a large bowl, combine olive oil, soy sauce, lemon juice, minced garlic, black pepper, and salt. Add the beef sirloin, cut into 1-inch cubes, and mix well. Cover and marinate in the refrigerator for at least 2 hours, or overnight for best results.

Prepare the Vegetables

While the beef is marinating, chop the bell peppers and onion into large pieces suitable for skewering.

Assemble the Skewers

Thread the marinated beef and chopped vegetables alternately onto the skewers. Leave a little space between each piece for even cooking.

Preheat the Grill

Preheat your grill to medium-high heat.

Grill the Shishkebabs

Place the skewers on the grill and cook for about 10-15 minutes, turning occasionally, until the beef is browned and cooked to your desired doneness.

Serve

Remove the skewers from the grill and let them rest for a few minutes. Serve warm with your favorite dipping sauce or side dishes.