Preheat the oven to 375°F (190°C).
Sauté the onion: Heat a medium skillet over low flame and add a splash of water. Cook the chopped onion until it becomes translucent, about 5 minutes.
Add mushrooms: Stir in the chopped mushrooms and toss to coat. Cook for about 5 minutes until they release moisture.
Season the filling: Sprinkle in onion powder, smoked paprika, garlic powder, nutritional yeast, and thyme leaves. Stir for a minute to toast the spices.
Deglaze: Pour in 1/3 cup white wine (or veggie broth) and cook until the liquid evaporates and the filling looks on the dry side.
Mix quinoa & sauce: Add the cooked quinoa and 2 tablespoons marinara to the mushroom mix. Stir to combine and adjust salt and pepper.
Prep peppers: Meanwhile, cut bell peppers in half lengthwise and remove cores and seeds. Arrange the halves in a baking dish.
Stuff peppers: Fill each pepper half with the mushroom–quinoa mixture. You should have just enough for 6 halves.
Assemble in pan: Spread half of the tomato sauce on the bottom of the pan. Place the stuffed peppers on top and spoon the remaining sauce over them. Optional: top each half with half a slice of vegan smoked gouda.
Cover & bake: Cover the pan with foil (or an oven-proof lid) and bake in the preheated oven for 1 hour.
Finish & serve: Garnish with chopped chives, parsley or microgreens, and drizzle with cashew aioli. Serve warm.
Pro tip: The long bake time lets flavors meld and prevents soggy peppers while yielding tender, roasted edges.
