To prepare spice mix, combine first 6 ingredients in a spice or coffee grinder; process until finely ground.
To prepare fish, combine mahimahi, turmeric, and 1/2 teaspoon salt in a large bowl; toss well. Heat 1 tablespoon oil in a large nonstick skillet over medium-high heat. Add half of fish; cook 5 minutes or until fish is lightly browned and flakes easily when tested with a fork (do not overcook). Remove from pan. Repeat procedure with remaining fish and oil.
To prepare sauce, add onion to pan; sauté 5 minutes or until tender. Add ginger, garlic, and bay leaf; sauté 2 minutes. Add ground spice mix; cook 2 minutes. Stir in water, 1 teaspoon salt, and sugar. Remove pan from heat; gradually stir in yogurt. Cook over low heat 5 minutes, stirring constantly. Return fish and accumulated juices to pan. Cook over low heat 5 minutes or just until heated. Discard bay leaf.