Place the water in a small non-stick skillet over medium heat.
Add the diced red onion and halved cherry tomatoes to the skillet, sautéing for about 5-7 minutes until the tomatoes soften and the water evaporates, creating a natural sauce.
Stir in the dried oregano, sea salt, and black pepper, then remove from the heat and cover to keep warm.
Fill a medium saucepan with water and add the apple cider vinegar, bringing it to a very gentle simmer over medium-low heat.
Crack each egg individually into a small ramekin, then carefully slide them into the simmering water one by one.
Poach the eggs for 3 to 4 minutes until the whites are opaque and set but the yolks remain soft.
While the eggs are poaching, toast the sugar-free sourdough slices until they are crisp and golden.
Place the toasted sourdough on a plate and top with the warm herbed tomato and onion mixture.
Use a slotted spoon to lift the poached eggs from the water, blot them gently with a paper towel to remove excess moisture, and place them on top of the tomatoes.
Garnish with freshly chopped parsley and serve immediately.