Cut the beef into 1” wide cubes.
Mix Marinade in a bowl. Add beef. Marinate for 1 - 24 hours, minimum 20 minutes.
Cut vegetables into 1" wide squares.
Thread beef (reserve Marinade), vegetables and mushrooms on each skewer alternating as desired. Thread loosely - don't smush together tightly (helps even cooking).
Brush kebabs lightly with Reserved Marinade (including vegetables), then drizzle with olive oil.
Heat BBQ or large skillet over high heat. Add 1 tbsp oil, then when smoking, cook kebabs in batches for 2 minutes on each side until slightly charred (4 sides = 8 minutes in total), basting with Reserved Marinade as you go.
Transfer to plate, cover loosely with foil and rest for 3 minutes before serving.