Heat cumin in oil in a 12-inch heavy skillet over medium heat, stirring occasionally, until fragrant, about 1 minute. Stir in tomatoes, capers, cinnamon, and 1/4 teaspoon each of salt and pepper and simmer, uncovered, stirring occasionally, until thickened, about 10 minutes.

Pat fish dry and sprinkle with 1/4 teaspoon each of salt and pepper, then add to skillet. Cover and simmer until fish is just cooked through, 7 to 10 minutes.