Heat a grill pan over medium-high heat and spray pan with nonstick cooking spray. Grill kebabs 3 minutes per side until medium-rare.
In a small bowl combine cucumbers and leftover reserved yogurt marinade.
Slice the top off the pita pockets. Fill the pockets with the beef, couscous and yogurt cucumber mixture. Place on serving dishes and serve.
In a large bowl whisk together canola oil, garlic, yogurt, cumin, salt, pepper and hot sauce. Reserve half the marinade, in a covered bowl, and refrigerate. Add beef cubes to remaining marinade, cover and refrigerate for anywhere from 30 minutes to overnight.
Preheat grill pan or outdoor grill to medium high heat. Be sure to oil the grill surface before grilling the kebabs.
Thread beef cubes and onion pieces onto skewers, alternating 3 pieces of beef and onion per skewer. Set aside extra beef cubes. Place skewers on the grill pan and cook 3 to 4 minutes on each side for medium-rare.
Place kebabs on a serving platter along with Spicy Couscous. Drizzle with some of the reserved marinade and serve.
Heat oil in a medium saucepan over medium-low heat. Saute garlic with red pepper flakes for 2 minutes being careful not to burn garlic. Add the chicken broth, turn up heat to medium-high and bring to a boil. Stir in couscous, cover and remove from the heat. Let stand 5 minutes. Season with salt and pepper and fluff with fork. Transfer to a serving bowl and serve.