Preheat the oven to 350 degrees F. Line a sheet pan with parchment paper.
To make a flax egg, mix together 1 tablespoon ground flaxseed and 3 tablespoons water in a small bowl. Let rest for 5 minutes.
Roughly chop the mushrooms and dice the onion. In a medium pan, heat 1 tablespoon olive oil over medium-high heat. Once hot, add the mushrooms and onion and sprinkle with ¼ teaspoon salt. Sauté for 5 minutes, or until mushrooms are softened. Drain excess liquid. Add the soy sauce and Italian seasoning and cook for a minute more.
Combine chickpeas, flax egg, breadcrumbs, nutritional yeast, Worcestershire sauce, and sautéed onion and mushrooms in a food processor with a standard blade attachment. Pulse until mostly broken down. Some small bits of chickpea or mushroom should still exist.
Use clean hands to roll the meatball mixture into 12 roughly ping pong sized balls. I find it's best if you flatten each ball into a patty and then roll it up. Line up the meatballs on the sheet pan. Spray lightly with cooking spray for an extra crispy/browned result (optional).
Bake for 30 minutes in a 350-degree oven, flipping meatballs over halfway through. They are done when lightly browned on the outside and no longer mushy on the inside.
Worcestershire sauce: Check the ingredients label to make sure your Worcestershire sauce is vegan/vegetarian. Most store-brand versions are made without anchovies, making them vegan.
How to freeze: I recommend cooking them (either baking or pan-frying) before freezing. Place in a freezer safe container with wax paper between layers. Freeze for up to 3 months. Let thaw overnight in the fridge or reheat in the microwave before cooking.
To make gluten-free: Choose gluten free breadcrumbs in place of traditional breadcrumbs. Gluten-free tamari can be used in place of soy sauce.
To pan-fry: Heat a large skillet over medium-high heat. Add a liberal amount of olive oil to the pan, enough to coat the entire bottom. Add the meatballs. Cook each side for about 1 minute. Optional: Add sauce and simmer until sauce is warmed through.
To shallow fry: Add about a half inch of canola oil to a hot skillet over medium-high heat. Once hot, add the meatballs and cook, stirring occasionally, until crisp and golden. I haven't tried deep frying these.
Storage and reheating: Keep refrigerated in a closed container for 3-4 days. Reheat in a lightly oiled skillet over medium-high heat or in the microwave until warmed through.