Prep the oven and pan. Heat oven to 375°F (190°C). Lightly oil a 9x13-inch baking dish or similar casserole pan.
Cook the bacon. In a large skillet over medium heat, cook bacon until crisp. Transfer to a paper towel–lined plate and crumble when cool.
Reserve 1 teaspoon bacon drippings in the pan if you like extra flavor.
Sauté the aromatics. Add 1 tablespoon olive oil (plus the bacon drippings if using) to the skillet. Cook onion with a pinch of salt until soft, about 4 minutes. Stir in garlic for 30 seconds until fragrant.
Soften the veggies. Add broccoli and cauliflower rice with 1/4 cup water.
Cook 4–5 minutes, stirring, until crisp-tender and most moisture evaporates. Set aside to cool slightly.
Blend the creamy base. In a bowl, whisk Greek yogurt, blended cottage cheese (or light cream cheese), chicken broth, lemon juice, and all ranch seasoning until smooth. Adjust salt and pepper to taste.
Combine the filling. In a large mixing bowl, toss chicken, sautéed veggies, half the crumbled bacon, 1/2 cup mozzarella, and Parmesan with the ranch-yogurt sauce until evenly coated.
Assemble. Spread the mixture in the baking dish.
Sprinkle with remaining mozzarella and bacon. Drizzle the last tablespoon olive oil lightly over the top for browning.
Bake. Bake 18–22 minutes, until hot and bubbling around the edges. Broil 1–2 minutes if you want a deeper golden top—watch closely.
Rest and serve. Let it sit 5 minutes to set.
Garnish with extra parsley or chives if you like. Serve warm.