Preheat oven to 180 °C.
Cut the peeled sweet potatoes into 2 cm chunks, and then place in an oven dish.
Sprinkle the sweet potatoes with half the chilli flakes, season with salt and pepper, then drizzle with 30ml of the olive oil. Roast in the oven for about 20 minutes, or until the sweet potato is tender.
Trim any excess fat off the steaks, then season with salt, pepper and the remaining chilli flakes.
Cook the steak in a searing hot pan for 2 minutes per side until browned, remove from the pan, then set aside to rest for 5 minutes. (Cook the steak for longer if you prefer it to be well done).
Once the steak has rested, slice it into thin strips.
Place the lentils, parsley, cherry tomatoes, red onion, baby spinach, sliced steak and roasted sweet potatoes into a bowl, then add the salad dressing and toss well.
Tip the salad onto a serving platter, then sprinkle with the feta cheese.