Vegetable oil spray
2 tablespoons extra-virgin olive oil
2 onions, minced
10 ounces white mushrooms, trimmed and sliced thin
1 green bell pepper, stemmed, seeded, and cut into ½-inch pieces
4 garlic cloves, minced
1 tablespoon minced fresh oregano or 1 teaspoon dried
1 (28-ounce) can crushed tomatoes
½ cup heavy cream
8 ounces ziti (2½ cups)
6 ounces sliced pepperoni
½ teaspoon salt
¼ teaspoon pepper
1 (15-ounce) can tomato sauce
Hot water, as needed
1 cup ricotta cheese (8 ounces)
1 cup shredded mozzarella cheese (4 ounces)
¼ cup chopped fresh basil
1. Line slow cooker with aluminum foil collar and coat with vegetable oil spray. Heat oil in large pot over medium-high heat until shimmering. Add onions, mushrooms, bell pepper, garlic, and oregano and cook until vegetables are softened and lightly browned, 8 to 10 minutes.
2. Stir in tomatoes and heavy cream, scraping up any browned bits, and simmer until thickened slightly, about 5 minutes. Stir in ziti, pepperoni, salt, and pepper.
3. Transfer ziti mixture to prepared slow cooker and spread tomato sauce evenly over pasta. Cover and cook until pasta is tender about 3 hours on high.
4. Remove foil collar. Gently stir pasta, adding hot water as needed to loosen sauce consistency. Dollop spoonfuls of ricotta over casserole, then sprinkle with mozzarella. Cover and let sit until cheese is melted, about 5 minutes. Sprinkle with basil before serving.