In a small bowl mix the tomato puree with the chilli and garlic, both grated on a fine grater and season with a pinch of salt. Spread this paste all over the steaks and set aside while you cook the potatoes in boiling water.
Preheat the grill to a high setting and cook the steaks for about 3 to 4 minutes on each side or until done to your liking.
When the potatoes are thoroughly cooked, drain well and shake the pan hard so that the potatoes split and release some steam. Squash them slightly with a fork. Add the butter or oil and return to the heat, add the spinach to the potato pot a handful at a time until it has wilted, season and serve with the spicy lamb.