Preheat oven to 375°F. Lightly oil a 9x13-inch baking dish.
Boil pasta in salted water until just shy of al dente. Drain and toss with olive oil.
Warm cream cheese, ranch, and pizza sauce in a saucepan over low heat. Whisk in garlic, oregano, salt, and pepper until smooth.
Combine pasta, chicken, bell pepper, onion, olives, half the mozzarella, half the cheddar, half the bacon, and half the pepperoni in a large bowl.
Pour the warm ranch sauce over the mixture and toss until everything is coated.
Spread into the prepared dish. Top with remaining cheeses, pepperoni, and bacon. Sprinkle red pepper flakes if using.
Bake until bubbling and lightly browned on top, 22–25 minutes. Broil 1–2 minutes for extra color if desired.
Rest 10 minutes, then garnish with parsley and serve warm.