Put a rimmed baking sheet under the broiler; preheat 5 minutes. Toss the pork with 1 tablespoon olive oil and 1 teaspoon fajita seasoning in a large bowl. Transfer the pork to the hot baking sheet and broil 5 minutes. Meanwhile, add the bell peppers, thickly sliced onions, 1 tablespoon olive oil and the remaining 1 teaspoon fajita seasoning to the bowl; toss.
Turn the pork and scatter the vegetables around it. Broil, tossing the vegetables and turning the pork occasionally, until the vegetables are tender and charred around the edges and a thermometer inserted into the center of the pork registers 145 degrees F, 5 to 7 minutes. Remove the pork to a cutting board and let rest 5 minutes. (Continue broiling the vegetables, if needed.)
Toss the thinly sliced onion, radishes, cucumbers, jalapenos and brine in a bowl; season with salt and pepper. Add the cilantro, the remaining 1 tablespoon olive oil and the lime juice; toss.
Slice the pork and toss with the peppers and onions. Serve in the tortillas with the cucumber salad and lime wedges.