Slice the avocado in half. Stab the pit with a knife and pull it free from the avocado. Scoop the innards from the skin and into a food processor. Add the chickpeas, parmesan, and garlic and pulse until the mixture breaks down into small chunks. Stream in the olive oil while pureeing until hummus is smooth and homogenous (or you can leave it a bit chunkier if you prefer). Pulse in salt & pepper to taste, then stir in the lemon or lime juice (this prevents browning). Serve with chips or pita bread. Store in fridge in an air-tight container for up to 3 days.