Put a heatproof serving platter on a rack in the center of the oven and heat the oven to 200 degrees F.

In a medium bowl, combine the beans, tomatillos, mango, red onion, lime juice, 1/3 cup of the vegetable oil, cilantro, and a few grinds of black pepper; toss gently. Let the salad sit at room temperature while you cook the fish.

Mix 1/4 teaspoon black pepper with the chili powder, cumin, oregano, and 1 teaspoon salt. Rub both sides of the tilapia fillets with the mixture. In a large (12-inch) nonstick skillet, heat the remaining 2 tablespoons of the oil over medium-high heat until hot. Cook two of the tilapia fillets until lightly browned and the flesh is opaque and cooked through, about 2 minutes on each side. Transfer the fish to the platter in the oven to keep warm while you cook the remaining two fillets. Transfer the fillets to the platter, and spoon half of the salad on top. Serve with the remaining salad on the side.

For a different spice combination, try rubbing the fish with Old Bay Seasoning. And for other salad combinations, try chickpeas or red beans in place of the black beans, and red tomato or cucumber in place of the tomatillo.