Make the pesto: Pulse the kale, cilantro, pistachios, parmesan, garlic and lemon zest and juice in a food processor until finely chopped. With the machine running, gradually add the olive oil and 1 tablespoon water and process until a chunky paste forms; season with salt and pepper.
Assemble the toasts: Spread 3 to 4 tablespoons of the pesto on each slice of bread. Very thinly slice the avocados and fan out decoratively on top of each piece of toast. Squeeze the lemon over the toasts and drizzle with olive oil. Sprinkle with sea salt and red pepper flakes.