Make the tomato-onion relish: heat 1 tablespoon of Sunflower Oil in a small saucepan over medium heat, then add one thinly sliced Onion and cook until soft and translucent, about 5 minutes.
Stir in one minced clove of Garlic and cook 30 seconds more, then add two chopped Tomato (or about 1 cup) and simmer until the tomatoes break down, 5–8 minutes.
Season the relish with 1 tablespoon White Vinegar, 1 teaspoon Sugar, and a pinch of Salt and Black Pepper; continue to simmer until slightly reduced and jammy, taste and adjust seasoning, then remove from the heat and keep warm.
Cook the sausage: heat a griddle or heavy frying pan over medium-high heat and add a little more sunflower oil if the pan is dry. Place the Boerewors in the pan and cook, turning occasionally, until well browned all over and cooked through, about 10–12 minutes (rest a couple minutes after cooking).
Toast the rolls: spread softened Butter onto the cut sides of the Hot Dog Rolls and toast them, cut-side down, in a dry skillet or under a broiler until golden and slightly crisp.
Assemble the rolls: place the cooked boerewors into each toasted roll, spoon generous amounts of the tomato-onion relish over the sausage, season with extra salt and pepper if desired, and serve immediately.
