Make the cashew “parm”: combine 3/4 cup raw cashews, 1/4 cup nutritional yeast, 1 teaspoon sea salt, 1 teaspoon lemon zest (optional), and 1/2 teaspoon garlic powder in a food processor and pulse until finely ground; set aside.
Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
Make the chia gel: stir 1 tablespoon ground chia or flax seeds with 3 tablespoons water in a small bowl and let sit until thickened, a few minutes.
Pulse the toasted pecans and 3/4 cup rolled oats in the food processor until you have a coarse meal, then transfer to a medium mixing bowl.
Heat 2 teaspoons olive oil in a large sauté pan over medium heat, add the diced small yellow onion and sauté 4–5 minutes until soft and translucent.
Add the sliced mushrooms to the pan, season with pepper, and cook about 5 minutes until tender and glossy; add 3 minced garlic cloves and cook 1 minute more, then season with salt and remove from heat.
Transfer the cooked mushroom mixture to the food processor, let cool slightly, and pulse until a chunky paste that will stick together (still with small pieces visible).
Combine the pulsed mushroom mixture with the pecan–oat mixture in the mixing bowl. Add 2 tablespoons nutritional yeast, 2 teaspoons balsamic vinegar, 1 teaspoon tamari, 1/2 teaspoon chili flakes, 1 teaspoon onion powder, 1 teaspoon garlic powder, 1/4 teaspoon liquid smoke, 1/3 cup chopped parsley, the chia gel, and a generous pinch of salt and pepper; mix thoroughly until sticky and slightly chunky, then taste and adjust seasoning.
Divide the mixture into 8 equal portions and roll into balls. Place on the prepared baking sheet, brush each ball with olive oil, and bake 25 minutes, or until firm and browned on the bottoms.
While meatballs bake, gently heat the marinara in a large saucepan or deep skillet so it is warm for serving.
When meatballs are done, transfer them into the warm marinara to heat together briefly.
Make the garlic oil: in a small saucepan over medium-low heat, warm 1/4 cup olive oil, add 3 finely minced (or grated) garlic cloves, salt, and optional chili flakes, and simmer very gently about 1 minute while stirring; remove from heat and stir in 1/4 cup chopped parsley.
Preheat the oven broiler. Slice the ciabatta baguette in half lengthwise, place cut side up on a baking sheet, brush evenly with the garlic–olive oil mixture, and broil 2–3 minutes until edges are browned and toasted—watch closely to avoid burning.
Cut the garlic bread into pieces, serve meatballs in warm marinara, sprinkle with cashew “parm” and extra parsley if desired, and enjoy.