Bring a large pot of salted water to a boil.

Add potatoes and cook until just tender, about 6 minutes.

Add colossal garlic cloves and simmer for 3 minutes more.

Drain and rinse garlic and potatoes under cold water; set aside.

Meanwhile, put soy sauce, oil, pepper, green onions, chopped garlic and orange juice into a wide, shallow dish and whisk to combine.

Transfer half of the marinade to a second wide shallow dish.

Arrange sirloin in one dish with marinade.

Arrange potatoes, colossal garlic, squash, mushrooms, red onions and tomatoes in second dish with marinade.

Cover both with plastic wrap.

Marinate both, turning the contents of each dish occasionally, for 4 hours. (Marinate the sirloin in the refrigerator and the vegetables at room temperature.)

Prepare a grill for medium heat cooking.

Thread vegetables and sirloin onto skewers, alternating them as you go, to form each kabob (if using wooden skewers, soak in water for 30 minutes before assembling).

Arrange skewers on grill, cover grill and cook, turning occasionally, until meat is cooked through and vegetables are tender.

Meanwhile, bring 3 cups of salted water to a boil in a medium pot.

Add couscous, return to a boil then reduce heat to low, cover and simmer for 2 minutes.

Set aside off of the heat to keep warm, then fluff couscous when ready to serve.

Arrange couscous on a large platter and top with skewers. Serve immediately.