Combine the chili powder, cayenne, and cumin then coat the tilapia (both sides) in the rub.
Heat the olive oil in a pan over medium heat, then cook the tilapia for 3 minutes per side. Remove from heat and chop or shred the fish fillets.
Add the scallions and garlic to the pan and cook until fragrant (about 30 seconds to 1 minute).
Add corn to the pan and stir, cooking the corn until it's slightly blackened.
Add the beans and cook 1 to 2 minutes (until the beans are warmed), then remove the pan from the heat.
Spoon the corn and bean mix into a soft taco tortilla, then top with tilapia. Add spicy fish taco sauce, lemon juice, cilantro, salt, and/or pepper to taste.