Cut fish into 8 equal portions. In a shallow dish whisk together the orange juice, honey, chopped jalapeno, and garlic. Add fish, turning to coat. Cover and let stand 15 minutes, turning once. Meanwhile, stir together the yogurt, cucumber, lemon juice, and 1/4 teaspoon salt; set aside.
Drain fish, discarding marinade. Sprinkle remaining salt over fish. Grill in a preheated grill pan (optional: line with foil) or on a gas or charcoal grill on the greased rack of a covered grill directly over medium heat for 4 to 6 minutes per 1/2-inch thickness or until fish flakes easily when tested with a fork, turning once.
Top each tortilla with fish. Serve with shredded lettuce, jalapeno slices, and/or orange zest, if desired, and top with yogurt mixture.