Coat a large nonstick staute pan with cooking spray.
Coat tilapia with blackened seasoning and cook over medium-high heat until fish flakes with a fork, about 2 to 3 minutes per side. (Do not crowd fish in pan. Only cook as much fish as can fit in a single layer. Cook in batches if necessary.)
Slice each radish in half and then thinly slice each half into half-moons.
In a medium bowl, combine radishes, cucumber, red pepper, scallions, cilantro, lime juice, and oil.
Season to taste with salt & pepper and serve over fish.