Preheat oven to 350 degrees. Line a rimmed baking sheet with parchment paper.
Start making polenta. Heat chicken or vegetable stock in a medium sauce pan over high heat. Bring to a boil and add dry polenta and fine sea salt. Cover and reduce to low heat.
Combine bell peppers, cucumber, red onion, garlic, oregano, bread crumbs, egg, ground black pepper, fine salt and ½ cup shredded mozzarella cheese in a large mixing bowl. Toss well.
Arrange portabella mushroom caps on the rimmed baking sheet. Baste with extra virgin olive oil.
Equally divide vegetable stuffing mix in each portabella cap.
Bake for 15 minutes.
Meanwhile, heat marinara sauce. Take polenta off heat and stir in butter. If it is too thick, add additional water and stir until desired consistency.
Plate by spooning polenta onto a plate, top with a stuffed portabella mushroom. Top with marinara sauce and remaining shredded mozzarella cheese.
Garnish with chopped parsley and Maldon sea salt.
If you've tried this recipe, come back and let us know how it was!