Heat a 12-in. nonstick frying pan over medium-high heat with 1 tbsp. oil. Rub halibut with 1/4 tsp. salt and 1/4 tsp. pepper. Lightly brown fish in frying pan on one side only, 3 to 4 minutes. Transfer to a plate.
Add remaining oil to frying pan along with fennel and ouzo. Cook, stirring frequently, until light golden and almost tender, about 8 minutes. Add garlic and cook, stirring, until fragrant, 1 minute.
Add tomatoes, 1/2 cup water, chickpeas, remaining salt and pepper, and the oregano and bring to a boil. Reduce heat to maintain a steady simmer. Lay halibut fillets, browned side up, in sauce and simmer until fish is cooked through, 5 to 10 minutes.