Place mushrooms in a bowl and cover with boiling water, approximately 2 cups. Steep for 30 minutes, then drain the mushrooms. Reserve the mushroom stock, which is extremely flavorful and can be used in whatever sauce you make with these meatballs.
Place the mushrooms in a food processor and process until they are finely shredded but not pasty. If the stems are tough even after soaking, discard them and use just the tops of the mushrooms.
Add walnuts and process them until they are broken into small bits but not powdered.
Add all of the remaining ingredients --chickpeas, garlic, ground cumin, smoked paprika, red pepper flakes, sage, soy sauce/tamari/Worcestershire sauce, and salt and black pepper to taste
Process or pulse a few times until the chickpeas are broken down and the mixture holds together firmly when you ball it up. If the ball falls apart after you form it, process the mixture further.
Remove the blade from the food processor bowl. Form 24 meatballs.
Place the meatballs in the air fryer basket. Preferably do this in two batches of 12 meatballs each so there is enough room for the air to circulate around the meatballs.
Spritz some cooking spray on the meatballs or brush on a bit of oil. If you want to make these completely oil-free you can leave out this step.
Click the air fryer basket into place. Set the air fryer to 375 degrees and air fry the meatballs for 14 minutes. About halfway through, open and rotate the balls so they cook evenly.