Preheat the oven to 250°C.
Slice the baby aubergines in half lengthways keeping the stalks attached.
Pour olive oil into a roasting tin, add dried oregano and aubergines, then toss to coat.
Arrange aubergines cut-side up and roast for 15 minutes until tender and golden.
Place sliced red onion in a bowl and cover with red wine vinegar and salt.
Transfer cooked aubergines to a platter.
Whisk extra-virgin olive oil, minced garlic, and cold water into the onion-vinegar mixture.
Pour the mixture over the warm aubergines and arrange the onions evenly.
Cool to room temperature for 30 minutes and garnish with fresh oregano before serving.