Prep the oven and pan: Preheat to 375°F (190°C). Lightly coat a 9x13-inch baking dish with cooking spray.
Cook the bacon: In a skillet, cook bacon until crisp.
Drain on paper towels and crumble. Reserve about 1 tablespoon bacon fat for the topping (or use olive oil).
Steam the broccoli: Microwave florets with a splash of water for 1–2 minutes until bright green and crisp-tender. Drain well to avoid watery casserole.
Make the creamy base: In a large bowl, whisk Greek yogurt, softened cream cheese, blended cottage cheese, and chicken broth until smooth.
Stir in ranch seasoning, garlic powder, onion powder, smoked paprika, black pepper, and optional red pepper flakes.
Add the cheeses: Fold in 1 cup cheddar, mozzarella, and Parmesan until evenly combined.
Combine the filling: Stir in the chicken, half the bacon, broccoli, and green onions until every piece is coated.
Assemble: Spread the mixture into the prepared baking dish. Sprinkle the remaining 1/2 cup cheddar on top.
Mix the crunchy topping: Toss panko with olive oil or reserved bacon fat and a pinch of paprika. Sprinkle evenly over the cheese.
Bake: Bake uncovered for 20–25 minutes, until the edges bubble and the top is golden.
If needed, broil for 1–2 minutes to crisp the topping. Watch closely.
Finish and serve: Let rest 5–10 minutes so it sets. Top with remaining crumbled bacon and extra green onions.
Serve warm.