Place the spinach, rocket, pecans, garlic, lemon juice and Pecorino in a food processor and blend. (You might have to do this in two batches as the spinach tends to be quite bulky and may fill up the bowl of the food processor too much.)
When the leaves are roughly choppes, slowly drizzle in the olive oil while the processor is still running.
Allow to blend until it forms a thick but moist pesto. Season to taste.
To serve, toss the pesto with cooked spaghetti and serve with grated Pecorino.
Store any left-over pesto in an airtight container in the fridge for up to 2 weeks.