½ cup soy sauce

⅓ cup vegetable oil

¼ cup lemon juice

1 clove garlic, minced

1 tablespoon prepared mustard

1 tablespoon Worcestershire sauce

1½ teaspoons salt, or to taste

1 teaspoon coarsely cracked black pepper

1½ pounds lean beef, cut into 1-inch cubes

16 mushroom caps

2 green bell peppers, cut into chunks

1 red bell pepper, cut into chunks

1 large onion, cut into large squares

8 metal skewers, or as needed

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Prepare the Marinade: In a bowl, whisk together the soy sauce, vegetable oil, lemon juice, minced garlic, mustard, Worcestershire sauce, salt, and black pepper.
Marinate the Beef: Place the beef cubes in a resealable plastic bag or shallow dish, pour the marinade over the beef, seal the bag or cover the dish, and refrigerate for at least 8 hours or overnight.
Marinate the Vegetables: Add the mushroom caps to the marinade during the last 2 hours of marinating to ensure they absorb the flavors.
Prepare the Skewers: Preheat your grill to medium-high heat. Thread the marinated beef, mushroom caps, bell peppers, and onion pieces alternately onto the skewers.
Grill the Kabobs: Place the skewers on the preheated grill and cook, turning occasionally, until the beef is browned and cooked to your desired level of doneness, about 10–15 minutes.
Serve: Remove the kabobs from the grill and let them rest for a few minutes before serving.

Optional: Add chopped jalapeños or a dash of hot sauce to the marinade for extra heat.

For a sweeter flavor, add honey or brown sugar to the marinade.

For an aromatic boost, add fresh herbs like rosemary or thyme to the marinade.