In a food processor, blend together spinach, basil, nuts, garlic, salt, pepper, lemon juice, lemon zest, and 3 tablespoons olive oil until smooth. Scrape down the sides of the bowl as necessary.
Pour in the remaining olive oil to the mixture until smooth. You can either leave the pesto chunky or process until smooth.
Store in an airtight container for up to 5 days.
Sandwiches
Place 4 slices of sourdough in a frying pan over medium heat and spread pesto evenly over all slices.
Place slices of mozzarella cheese, tomato and roasted red peppers on top of two bread slices and allow the cheese to melt and the veggies to soften slightly.
Place the slices of sourdough with just the pesto on top of the other 2 slices and remove from the frying pan. Cut and serve immediately!
Notes
You could also make this sandwich in a toaster oven or a panini maker.