1. Bring 3/4 cup water to a boil in a small saucepan; gradually stir in couscous. Remove from heat; cover and let stand 5 minutes. Fluff with a fork.
2. While couscous stands, remove casings from sausage. Cook sausage in a medium nonstick skillet over medium-high heat 4 minutes or until browned, stirring to crumble. Remove from heat. Stir in couscous, 1/4 teaspoon salt, and pepper. Stir in 6 tablespoons cheese.
3. Cut tops off bell peppers; reserve tops. Discard seeds and membranes. Sprinkle remaining 1/4 teaspoon salt evenly inside peppers. Divide sausage mixture evenly among peppers. Replace tops of peppers. Place stuffed peppers in a 5-quart round electric slow cooker. Cover and cook on LOW for 4 hours or until peppers are tender.
4. Top peppers evenly with remaining 2 tablespoons cheese and, if desired, sprinkle evenly with basil.