Preheat and prep the pan. Heat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with cooking spray or a thin layer of olive oil.
Cook the veggies. Warm 1 tbsp olive oil in a skillet over medium heat.
Add diced celery and carrots with a pinch of salt and pepper. Sauté 5–7 minutes until slightly softened. Remove from heat and let cool a bit.
Make the creamy buffalo base. In a large bowl, whisk together Greek yogurt, light cream cheese, egg whites, buffalo sauce, garlic powder, onion powder, smoked paprika, and black pepper.
Taste and adjust heat with more buffalo sauce if needed.
Add the chicken and veg. Fold in the shredded chicken, sautéed vegetables, and half the green onions. Mix until everything is evenly coated.
Layer in the dish. Spread the mixture into the prepared baking dish. Sprinkle evenly with the mozzarella and cheddar.
Bake. Place on the center rack and bake for 22–28 minutes, until the edges are bubbling and the cheese is melted and lightly golden.
If you like a deeper color, broil for 1–2 minutes at the end, watching closely.
Finish and garnish. Let the bake rest for 5 minutes. Top with remaining green onions and a light sprinkle of blue cheese crumbles if using. Add a drizzle of ranch or blue cheese dressing for extra tang, or serve on the side.
Serve. Scoop into bowls or plates.
It’s great on its own or over cauliflower rice, brown rice, or a bed of shredded lettuce for a buffalo “bowl” vibe.