In my opinion, pesto has to be about preference, so I'm only going to give you a rough guide of what to look for. If you are eager to be more authentic in the process, this can be done in with a mortar and pestle. Otherwise, use a blender or food processor.
Add the Bärlauch to the processor with a few tablespoons or estimated rounds of olive oil, a palm-full (or more, depending on how much greens you are using) of nuts, a few squeezes of lemon juice, a few twists or pinches of salt and pepper, and less than a palm-full of Parmigiano. Begin to blend.
Use your eyes and ears - if the processor becomes 'stuck', you do not have enough liquid, so add more olive oil.