Soak walnuts in lukewarm water for 20 minutes to soften. Drain and set aside
In a medium nonstick pan over medium heat, add the onions and garlic along with 2-3 tablespoons of water. Cook, stirring often until the onions are translucent and the garlic is fragrant about 3-4 minutes. Add 2-3 more tablespoons of water as needed to prevent burning. You can also use oil instead if you would like.
Add the walnuts and mushrooms to a food processor and pulse until they have broken down into a “meat crumble”-like texture. Add them to the pan along with the cumin, chili powder, tomato paste, soy sauce, oregano, liquid smoke, and 1/4 cup of water. Mix everything together until well combined. Cook the mixture for 8 minutes, or until it beings to brown and the mushrooms soften. If you would like it moister, add a few additional tablespoons of water as desired.
Remove from heat and season with salt and pepper as desired. Mix through the cilantro plus lime juice to taste.
Assemble your tacos as desired and enjoy!