Preheat the oven to 450 degrees . In a liquid measuring cup, whisk together the orange juice, vinegar, sugar and 1/2 teaspoon salt. Whisk in 2 tablespoons olive oil; set aside.
In a medium bowl, toss the jicama and orange pieces. Dress the slaw with about one-third of the orange juice mixture, toss with the mint and season with salt; set aside.
Whisk the remaining 1/4 cup olive oil into the remaining orange juice mixture and stir in the garlic. Brush the bottom of a medium baking dish with some of the garlic-orange juice mixture. Season the fillets on both sides with salt and transfer to the dish. Pour the remaining garlic-orange juice mixture on top. Bake until opaque, about 6 minutes. Serve with the reserved slaw.