Preheat oven to 350 degrees.
Place orange juice, olive oil, salt, red pepper flakes, cumin, and lemon zest and juice in a medium bowl; whisk until well combined.
Place fennel in a baking dish just large enough to fit fennel in an even layer; pour over orange juice mixture. Cover with parchment-paper-lined aluminum foil and transfer to oven. Bake for 35 minutes, uncover, and continue baking until fennel is golden brown, about 10 minutes more. Remove from oven; serve warm or at room temperature.