1. Preheat the oven to 350°F (175°C) and lightly grease a 9×13-inch baking dish with nonstick cooking spray.

2. Brown the ground beef in a large skillet over medium-high heat, breaking it up with a spoon until no pink remains, 5 to 7 minutes; drain excess grease if needed.

3. Add the diced yellow onion and green bell pepper to the skillet and cook for 3 to 4 minutes, stirring often, until the vegetables soften.

4. Stir in the minced garlic, Italian seasoning, kosher salt, freshly ground black pepper, and crushed red pepper flakes; cook for 30 seconds until fragrant.

5. Pour in the pizza sauce or marinara, stir to coat the meat and vegetables, and let the mixture simmer for 2 to 3 minutes, then remove from the heat.

6. Cut each refrigerated biscuit into quarters and place the biscuit pieces in a large mixing bowl.

7. Pour the warm meat and sauce mixture over the biscuit pieces, add half of the shredded mozzarella and half of the shredded cheddar cheese, and gently toss until everything is evenly coated.

8. Spread the biscuit mixture into the prepared baking dish in an even layer.

9. Sprinkle the remaining mozzarella and cheddar over the top, then scatter the sliced pepperoni and finish with the grated Parmesan.

10. Bake for 30 to 35 minutes, or until the biscuits have puffed, the sauce is bubbling around the edges, and the top is golden brown.

11. Let the casserole rest for 5 to 10 minutes, then sprinkle with chopped fresh parsley and serve warm.