To prepare ponzu, place 1/2 cup orange juice and the next 5 ingredients (through 1 1/2 chipotle chiles) in a blender, and process until smooth.
To prepare salsa, combine diced cucumber, tomato, avocado, and cilantro in a small bowl.
Sprinkle fish with salt. Heat a large nonstick grill pan over medium-high heat. Coat pan with cooking spray. Add fish; cook 3 minutes on each side or until desired degree of doneness. Cut each tuna steak diagonally across the grain into thin slices. Arrange sliced tuna over rice; top with salsa, and drizzle with ponzu.