Place the tilapia on a plate. Rub 1 tablespoon of the vegetable oil onto both sides of the tilapia filets.
Spoon the homemade blackened seasoning over the fish and spread around (both sides). I use about ½ tablespoon per fish. You can adjust the seasoning amount based on your preference. The more you use, the spicier it will be and the less you use, the milder it will be.
Heat the remaining vegetable oil over high heat in a cast iron skillet.
Place tilapia on the hot cast iron pan and let it cook for 3 minutes. Time it and don't move the fish, so it can get that beautiful blackened crust on it.
Flip and cook another 2-3 minutes until the tilapia has an internal temperature of at least 145 degrees F.
Remove to a separate plate and allow it to cool for a few minutes. Serve warm and enjoy!
Notes
Refrigerate the leftovers in an air tight container for up to 4 days.