Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with the olive oil and set it aside.

Place a large skillet over medium-high heat and add the ground beef. Cook, breaking it up with a spatula, until browned and cooked through, about 6–8 minutes.

Drain any excess fat from the skillet, then return the cooked ground beef to medium heat.

Stir in the pizza sauce, Italian seasoning, garlic powder, salt, and black pepper. Let the mixture simmer for 2–3 minutes, stirring occasionally, then remove from heat.

Open the can of refrigerated biscuit dough. Separate the biscuits and cut each biscuit into 6 to 8 small pieces, roughly bite-sized.

Add the biscuit pieces to the skillet with the warm beef and sauce mixture. Gently fold everything together until all of the biscuit pieces are well coated in sauce.

Transfer the biscuit and beef mixture into the prepared 9x13-inch baking dish, spreading it out evenly in the pan.

Sprinkle the diced green bell pepper and diced red onion evenly over the top of the biscuit mixture.

Scatter the sliced pepperoni over the vegetables, distributing it so each serving will get some.

Sprinkle the shredded mozzarella cheese evenly over the top, followed by the shredded cheddar cheese.

Place the baking dish in the preheated oven and bake for 25–30 minutes, or until the biscuits have bubbled up and are cooked through and the cheese is melted and lightly golden in spots.

Remove the Bubble Up Biscuit Pizza Casserole from the oven and let it rest for about 5–10 minutes so it can set slightly, then slice into portions and serve warm.