½cucumberpeeled, halved lengthwise, seeded, and cut into thin half moons
½red onioncut into wedges, then slivered
2tablespoonsfresh lemon juice
86-inch flour or corn tortillas
Crumbled queso fresco to serve
Heat a large heavy skillet, preferably nonstick, over medium high heat. Add one tablespoon of the oil. While the oil is heating, sprinkle both sides of the fish filets with the coriander, cumin, salt and pepper. Sear the fish for about 3 minutes per side, until browned and cooked through. Transfer the fish to a plate and break it into small chunks. Tent with foil to keep warm. Wash the skillet out.
While the fish is cooking combine the radishes, cucumbers, red onion, fennel, olives (if using), lemon juice and the remaining tablespoon of oil. Season with salt and pepper.
Return the clean, dry skillet to medium high heat and cook the tortillas for about 20 seconds on each side for flour, 45 seconds on each side for corn, until lightly browned in spots and softened. Stack them on a plate.
Serve the tortillas with the fish, and the vegetable relish, along with the queso fresco on the side. Let everyone assemble their own tacos.