In a small bowl, mix together paprika, chili powder, cumin, garlic powder, onion powder, salt, and pepper to make the blackening seasoning.
Pat tilapia fillet dry with a paper towel, then coat both sides evenly with the spice mixture.
Heat olive oil in a nonstick skillet over medium-high heat.
Place the tilapia fillet in the skillet and cook for 3–4 minutes per side, or until the fish is blackened and cooked through. Remove from heat and set aside.
In a medium bowl, combine cucumber, avocado, jalapeño, red onion, cilantro, and lime juice. Stir gently to combine.
Taste and adjust seasoning with salt or lime juice, if needed.
Serve the blackened tilapia hot, topped with a generous spoonful of cucumber avocado salsa.
Garnish with fresh cilantro or a lime wedge before serving.