Smash the oregano and salt into a paste in a mortar and pestle. (Or use food processor) Gradually work in the olive oil, and then the lemon juice.
Toss the lentils with 2 tablespoons of the oregano oil, taste, and season if needed. Arrange on a platter or in a bowl. Just before serving, cut the avocado into quarters, then slice quite thinly, and arrange on top of the lentils. Drizzle with a bit more of the oil, and sprinkle with the hazelnuts, and chives. A final drizzle of oil might be needed, and perhaps a bit more lemon juice.