Slice the onion into rounds and spread it across the bottom of the tagine.
Rinse the chicken pieces and arrange them directly on top of the onion layer.
Cut the sweet potato and carrots into thick wedges and fan them over the chicken, toward the edges of the tagine.
Nestle the hot peppers among the vegetables, add the tomato wedges, scatter the peas, and tuck in the celery-parsley bundle.
Sprinkle the black pepper, turmeric, ginger, Sudani spice, garlic powder and salt evenly over everything, then drizzle with the oil.
Pour about a cup of water gently around the edge of the tagine, not directly over the spices.
Cover and cook over the gentlest heat for about 1 to 1.5 hours, until the chicken and vegetables are tender.
Serve straight from the tagine with warm bread and olives.