How to Make It
In a blender, combine the citrus zests and juice with the 2 tablespoons of olive oil, the garlic, oregano, cumin, 1 1/4 teaspoons salt and 1/2 teaspoon pepper and blend until smooth.
In a glass or ceramic baking dish, pour all but ¼ cup of the marinade over the steak and turn to coat. Let stand for 15 minutes, or cover with plastic wrap and refrigerate for up to 24 hours.
Light a grill or grill pan and oil the grate. Remove the steak from the marinade, letting the excess drip off. Season with salt and pepper and grill over moderate heat, turning once, until lightly charred and an instant-read thermometer inserted in the thickest part registers 125°, 10 to 12 minutes. Transfer the steak to a carving board and let rest for 5 minutes. Thinly slice the meat against the grain and transfer to a platter with the mango slices and lime wedges. Drizzle with the reserved marinade and serve.