1 cup margarita mix
1/2 teaspoon salt
1 tablespoon white sugar
2 cloves garlic, minced
1/4 cup vegetable oil
1 pound top sirloin steak, cut into 1 1/2-inch cubes
8 metal skewers, or bamboo skewers soaked in water for 30 minutes
16 mushrooms, stems trimmed
1 onion, cut into 1-inch chunks
1 large red or green bell pepper, cut into 1 inch pieces
Combine margarita mix, salt, sugar, garlic, and vegetable oil in a bowl or resealable plastic bag. Toss sirloin cubes in marinade and marinate at least 30 minutes.
Preheat a grill for medium heat.
Assemble skewers, alternating meat with mushrooms, onion, and bell pepper. Brush skewers with marinade, then discard the remaining marinade. Grill skewers to desired doneness, about 10 minutes total for medium.