To make the marinade, place the garlic, red wine vinegar, Worcestershire sauce, cumin seeds, and chili flakes in a small dish and whisk to combine.
Place the steak pieces in a large, sealable freezer bag. Pour the marinade over the steak and seal the bag tightly. Gently turn the bag to make sure the steak is uniformly covered. Place in refrigerator for 2 hours to marinate or overnight if possible. Remove from the fridge 1 hour before cooking to come to room temperature.
About an hour before ready to enjoy this dish, bake the sweet potatoes in a preheated oven 220C/425F/Gas 7 for 45 minutes, or until soft.
To make the salad, toss together the red onion, sweetcorn, and tomatoes. Sprinkle with parsley and crumbled feta. Place in the fridge till needed.
To make the aji sauce, place all the ingredients in a bowl and stir to combine. Place in the fridge till needed.
The steak can be cooked under the grill/broiler or on a barbecue grill (gas or charcoal). Preheat cooking device to hot.
Remove steak from marinade and pat dry with a paper towel. Thread onto 4 pairs of metal skewers.
Grill for 3-4 minutes on each side or to your preferred steak doneness.
Remove from heat, cover, and rest for 5-10 minutes.
Divide the tomato salad between 4 plates, add and allow one double skewer of steak, and one baked sweet potato per plate. Drizzle with one-quarter of the aji sauce. Enjoy!