Cut the sirloin into pieces about 1 inch in size and add them to a large resealable bag.
1 pound beef sirloin
Pour the marinade into the bag with the steak. Seal it and put in the refrigerator to allow the steak to marinade. Let it marinade for at least 30 minutes, although I prefer at least 3 hours for tenderizing the steak.
If you are using wooden skewers put them in water to soak for 30 minutes before making the kabobs.
When you are almost ready to cook cut the mushrooms, bell peppers and onions into pieces about 1 inch in size.
8 ounces mushrooms, 1 bell pepper, 1 red onion
Put the vegetables in a bowl and drizzle with the olive oil. Season with a little salt and pepper.
1 Tablespoon olive oil, salt and pepper to taste
Take the steak out of the bag and discard the marinade.
Thread the steak and vegetables onto the skewers.
Cook the skewers on a grill at medium high heat. Turn them once or twice during cooking so the steak kabobs brown evenly. Remember that metal skewers will get very hot and handle with a hot pad. The kabobs will cook in about 10-12 minutes. Check and make sure the steak has reached 145 internally before serving.
Notes
The more uniform the cubes of meat and vegetables are the easier it is to get consistently cooked kabobs.
Watch the kabobs on the grill closely, so they don't flame up and over cook.
Serve with garlic aioli sauce or steak sauce for dipping.