Heat oil in 10 inch non-stick skillet over high heat. Add onion and garlic and cook until fragrant, about 1 minute. Add celery and fennel seeds. Cook about 2 more minutes. Stir in tomatoes, water, orzo, olives and capers, some of the salt and pepper. Bring to a boil and reduce heat. Cover and simmer 5 minutes. Season halibut with remaining salt and pepper and add to skillet, spooning the mixture over the fish. Cover and simmer until the fish is opaque in center and the orzo is tender, about 10-12 minutes.