Toast the Walnuts:
Preheat a dry skillet over medium heat. Add the walnuts and toast for 3-4 minutes, stirring frequently, until fragrant. Remove from heat and set aside to cool.
Sauté the Vegetables:
Heat the olive oil in a skillet over medium heat. Add the onion and garlic, cooking until softened, about 3-4 minutes.
Add the mushrooms and cook until they release their moisture and begin to brown, about 6-8 minutes. Remove from heat.
Blend the Pâté:
In a food processor, combine the toasted walnuts, sautéed vegetables, miso paste, soy sauce, nutritional yeast, smoked paprika (if using), and black pepper.
Blend until smooth, stopping to scrape down the sides as needed. Add water, one tablespoon at a time, to achieve a creamy and spreadable consistency.
Add Fresh Herbs:
Add the chopped parsley and pulse briefly to incorporate.
Serve:
Transfer the pâté to a serving dish. Garnish with additional parsley and a drizzle of olive oil if desired. Serve with crackers, crusty bread, or fresh vegetables.