Preheat oven to 425°F. Halve bell peppers lengthwise, remove seeds and ribs, and place them cut side up in a baking dish. Drizzle with 1 teaspoon oil, sprinkle with salt and black pepper, then turn them cut side down.
Roast peppers until just tender, about 12 minutes. Carefully turn peppers cut side up.
In a large bowl, beat egg, then add turkey, scallions, couscous, mint, parsley, coriander, cumin, turmeric, cinnamon, cayenne, 1 teaspoon garlic, and 1 tablespoon water. Mix well.
Divide turkey mixture among peppers, drizzle with 1 tablespoon water and remaining oil, then cover with foil.
Bake until filling is cooked through, about 35 minutes. Uncover, baste peppers with juices, and bake for an additional 5 minutes until lightly browned.
Meanwhile, mix mayonnaise, sour cream, lemon juice, 2 tablespoons water, remaining garlic, salt, and pepper in a small bowl.
Top peppers with tomatoes, mint, and parsley, and serve with mayo sauce on the side. Enjoy your delicious creation!