Cut red onion into 4 wedges, leaving root end intact. Place red onion, bell peppers, vinegar, 1/4 teaspoon salt, and 1/2 teaspoon oil in a zip-top plastic bag. Seal bag; toss well to coat.
Heat 1/2 teaspoon oil in a large nonstick skillet over medium-high heat. Add chopped onion and garlic; sauté 3 minutes. Add cumin, fennel, and cinnamon; sauté 1 minute. Add 1/4 teaspoon salt, 1/4 cup water, olives, raisins, black pepper, tomatoes, and potatoes; bring to a boil. Cover, reduce heat, and simmer 25 minutes or until potatoes are just tender.
Remove bell peppers and red onion from bag, discarding marinade; place on grill rack coated with cooking spray. Grill 10 minutes, turning frequently.
Bring 1 cup of water to a boil in a medium saucepan; gradually stir in couscous. Remove from heat; cover and let stand 5 minutes. Fluff with a fork. Serve tomato mixture over couscous. Top with grilled bell peppers and red onions; sprinkle with pine nuts.