Brush the lamb fillets with sesame oil. Season with salt and pepper. Preheat the oven to 220ºC. Toss the pumpkin with olive oil and a little sea salt, roast for about 20 minutes.
Preheat a non-stick pan to moderately hot. Keep the heat at moderately high. Cook one side of lamb fillet until the first sign of moisture appears on the uncooked side, turn and cook other side. You may need to turn the meat 3 times so all sides are browned.
Test for doneness with tongs. Rare is soft when pressed, medium is springy and well done is very firm. Rest the lamb for 2 minutes before slicing.
To serve, place spinach leaves on plate, add a little roasted pumpkin, sprinkle with crumbled feta and black olives, dress with a little olive oil. Place thinly sliced lamb on top.
