Preheat the oven to 400°F (200°C). Brush the portobello caps all over with 1 tablespoon olive oil and season with salt and pepper. Finely chop the reserved stems.
Place the mushroom caps gill-side down on a lined baking sheet and roast 10 minutes to release excess moisture. Flip gill-side up and set aside.
Meanwhile, heat the remaining olive oil in a skillet over medium heat. Add the onion and chopped mushroom stems and cook 5-6 minutes until softened. Add garlic and thyme and cook 1 minute.
Stir in the spinach and cook 2 minutes until wilted. Add the lentils, walnuts, sun-dried tomatoes, and balsamic vinegar. Cook 2-3 minutes to combine and heat through. Season with salt and pepper.
Divide the filling among the mushroom caps, mounding it on top. Return to the oven and bake 12-15 minutes until heated through and the mushrooms are tender.
Drizzle with a little extra balsamic vinegar and scatter fresh parsley over the top before serving.
Kept Recipes turns anything — a screenshot, a webpage, a craving — into a clean cookbook page like this one. No ads, no accounts, yours to keep.
Get the app