Preheat oven to 150°C. Lightly brush a 1L (4-cup) capacity non-stick loaf pan with oil to grease. Line the base and 2 long sides with non-stick baking paper, allowing sides to overhang.
Place the ricotta, egg, parmesan and lemon rind in the bowl of a food processor. Season with salt and pepper. Process until smooth. Spoon the mixture into the prepared pan and use the back of the spoon to smooth the surface.
Place the loaf pan in a large roasting pan. Pour enough boiling water into the roasting pan to reach halfway up the sides of the loaf pan. Bake for 1 hour or until the ricotta is firm.
Remove the loaf pan from the roasting pan and set aside for 20 minutes to cool slightly. Turn the ricotta onto a plate. Set aside for 1 hour to cool completely.
Meanwhile, preheat grill on high. Place the tomato, cut-side up, on a baking tray. Season with salt and pepper. Cook under grill for 5 minutes or until the tomato is soft and charred. Set aside for 30 minutes or until cool. Halve lengthways.
While the tomato is cooling, place the oil, chives and a pinch of salt in the jug of a blender and blend until smooth and bright green. Strain through a fine sieve lined with muslin into a jug.
Slice the ricotta loaf. Divide the ricotta, tomato and avocado among serving plates. Top with baby rocket leaves. Drizzle over the chive oil to serve.