Fill a medium saucepan with water and bring it to a very gentle simmer over medium-low heat without adding any vinegar.
Place a small non-stick skillet over medium heat with the extra virgin olive oil.
Add the diced red onion and halved cherry tomatoes to the skillet, sautéing for about 5-7 minutes until the tomatoes soften and blister.
Stir in the dried oregano, sea salt, and black pepper, then remove from the heat and cover to keep warm.
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 and runny.
While the eggs are poaching, toast the sourdough slices until they are crisp and golden, then top with the creamy sliced avocado.
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 crumbled feta cheese and freshly chopped parsley and serve immediately.