Preheat oven to 400°. Discard pepper seeds and membranes. Stand peppers on end on a baking sheet. Bake 15 minutes or until tender.
Meanwhile, cook couscous according to package directions, using chicken broth instead of water. Crumble meatloaf; cook in hot oil in a nonstick skillet over medium-high heat, stirring gently, 3 minutes. Toss nuts, next 2 ingredients, and meatloaf mixture with couscous. Add salt and pepper to taste. Divide couscous mixture among peppers (about 1/2 cup each).
Bake at 400° for 15 minutes or until peppers are very tender. Increase oven temperature to broil, with oven rack 7 inches from heat. Combine cheeses, and sprinkle over peppers. Broil peppers 2 to 4 minutes or until cheese melts and begins to brown.