To make spice marinade, combine all ingredients in a large bowl. Add beef and rub in marinade. Refrigerate, covered, for several hours or overnight.
To make yoghurt mint sauce, process all ingredients until smooth.
To make mash, preheat oven to 200C.
Place potatoes in a deep baking dish. Season. Zest lime and set zest aside until later. Cut lime in half and place, cut side down, on top of potatoes. Cover dish tightly with foil. Roast for 30 minutes or until very tender. Remove foil being careful of escaping steam. Squeeze cooked limes over potatoes. Mash. Add reserved lime zest and remaining ingredients. Mash to combine.
Place tomatoes on an oven tray. Drizzle with oil and season. Roast for 15-20 minutes or until tender, charred and split.
Bring steaks to room temperature. Season with salt. Heat half the oil and butter in a large frying pan over medium-high heat. Cook two of the steaks for 2-3 minutes on each side. Transfer to a warm plate and stand for 5 minutes. Wipe pan clean. Repeat with remaining steaks.