Remove the fillet steak from the fridge and let it sit at room temperature for 15 minutes. Grate the fennel into a small bowl. Pour the umeboshi and mirin over the fennel and stir through. Cover with a smaller dish and weight it down to "cook" in the vinegar. In a heavy based non stick frying pan dry roast the slivered almonds under a medium flame until they turn slightly golden in colour. Remove from the heat and set aside.
Brush the steak with olive oil. Heat the pan and add the steak. Cook for 4 - 5 minutes each side according to your preference. Remove the steak and while the pan is still hot toss in the rocket leaves and toss around until they are slightly wilted. Drain the fennel and serve it over the steak on a bed a bed of rocket with almonds.