In a large skillet, heat 2 tbsp. EVOO over medium-high heat. Add the mushrooms and cook until nicely browned, about 5 minutes. Add the onion, lower the heat to medium and cook, stirring, until golden and tender, about 5 minutes; transfer to a plate.
In the same pan, heat the remaining 2 tbsp. EVOO over medium heat. Add the bell pepper and cook for 2 minutes. Add the sausage, crumbling with a wooden spoon, and cook over medium high heat, stirring occasionally, until browned, about 3 minutes. Remove from the heat.
Position a rack in the center of the oven and preheat to 400 degrees . Lightly grease an 8-inch square glass baking dish and add 1 cup marinara to the bottom, tilting to coat. Top with 1 matzo. Break off a piece from another matzo to evenly cover the bottom. Layer on 1/2 cup marinara, the mushroom mixture, half the ricotta, 1/2 cup marinara and 1/2 cup mozzarella.
Add another layer of matzo, 1 cup marinara, the sausage mixture, the remaining ricotta, 1/2 cup marinara and a final layer of matzo. Top with the remaining 1/2 cup marinara and 1 cup mozzarella, then with the pepperoni and oregano.
Cover snugly with foil, set on a baking sheet and bake for 30 minutes. Uncover the pan and bake until golden and bubbling, about 15 minutes. Let cool for 20 minutes before cutting.