Prepare the ribs: Preheat your oven to 160°C. Pat the spareribs dry with paper towel. Mix the salt, black pepper, smoked paprika, garlic powder, and onion powder together and rub the spice mixture all over the ribs, coating both sides evenly. Drizzle with oil and rub in to help the spices adhere.
Slow-bake the ribs: Place the ribs meat-side down in a large roasting tray. Cover tightly with foil and bake for 2 hours, or until the meat is tender and beginning to pull away from the bones.
Make the glaze: While the ribs are baking, combine the tomato sauce, soy sauce, honey, brown sugar, apple cider vinegar, crushed garlic, and chilli flakes in a small saucepan over medium heat. Stir well and simmer for 5 minutes until the glaze thickens slightly. Remove from the heat and set aside.
Glaze and finish the ribs: Remove the ribs from the oven and increase the temperature to 200°C. Discard the foil and flip the ribs meat-side up. Brush generously with the glaze and return to the oven uncovered. Bake for 20-30 minutes, brushing with more glaze every 10 minutes, until the ribs are sticky, caramelised, and deep golden brown.
Rest and serve: Remove the ribs from the oven and allow them to rest for 5-10 minutes before cutting into individual ribs. Serve with any remaining warm glaze on the side.