In a bowl, combine the yogurt, 1 teaspoon salt, black pepper, mixed spices, nutmeg, 1 garlic clove, 1 tablespoon vinegar, and juice of 1 lemon. Mix well, then add the chicken cut into shawarma-style strips. Stir to coat and let marinate for a while.

Slice the onions into thin strips (julienne). Cut the bell peppers and tomatoes into thin strips as well and set aside.

Heat a skillet over high heat. Add the marinated chicken and do not stir at first to prevent it from releasing too much liquid. Sauté until the color changes, then add the onions. Once the chicken is nearly cooked, add the bell peppers and toss briefly so the peppers stay crisp. Remove from heat.

For the garlic sauce: In a small bowl, mix 3 tablespoons yogurt with 3 tablespoons mayonnaise (equal parts), a pinch of salt, 1 garlic clove (minced), juice of 1 lemon, and a splash of vinegar. Stir well for a quick and delicious garlic sauce.