Place kale leaves in colander in sink. "Flash blanch" the kale by pouring boiling water over the kale, then immediately rinse the kale with the coldest water from the tap. If you are making pasta, you can do double duty and drain the pasta and boiling water in a colander over the kale.
Smash garlic cloves and remove green stem inside. Add garlic, pepitas, nutritional yeast, lemon juice, lemon zest if using, and salt in food processor or high power blender. Chop in food processor until roughly chopped, stopping machine to scrape bits off sides and back down into food processor or blender bowl.
Tightly squeeze as much water as you can from the blanched kale. Add kale and to the food processor or blender. Pulse until combined. Everything will still look pretty choppy.
With the food processor running, drizzle olive oil until the pesto is the consistency you want. I like my pesto on the thicker side, spreadable as opposed to pourable.
Taste and add more salt or lemon juice as needed. Remember that straight pesto out of the food processor should taste saltier than is "comfortable" for you. The flavor will dilute when you add it to pasta, or whatever dish you're using it on.
Pesto keeps for about three days in an air-tight container in the refrigerator. It will darken in color after 1 day, but it will be fine to eat.