Add basil, avocado, garlic, pine nuts and lemon juice to a food processor and pulse for 20 seconds or until pesto is chopped. Add in water and process again until completely smooth. You may need to add more water to get it to your desired consistency; I like mine a little on the thicker side. Transfer to a bowl and stir in the cheese.
Store in an airtight container or sealed mason jar and refrigerate. Pesto is best if used within a few days, otherwise you can freeze it for several months. Makes 1 cup, or 2-4 servings depending on what it's used for.
Notes
Toss in 1/2 cup spinach for extra nutritionYou can omit the pine nuts, but I think they add a nice flavor.