Boil pasta in salted water until al dente. Reserve 1/2 cup cooking water; drain.
Pat chicken dry. Season with salt, pepper, and garlic powder.
Heat olive oil in a large skillet over medium-high heat.
Sear chicken until browned and cooked through, about 6 minutes per side.
Rest chicken 5 minutes, then chop into bite-size pieces.
Melt butter in the same skillet over medium heat. Add garlic; cook 30 seconds.
Stir in hot sauce and broth. Simmer two minutes, scraping browned bits.
Whisk in cream cheese until smooth. Pour in heavy cream; simmer to thicken.
Add cheddar and mozzarella. Stir until melted and glossy.
Fold in pasta and chopped chicken. Loosen with pasta water if needed.
Taste and adjust seasoning. Stir in celery if using.
Top with green onions and blue cheese. Drizzle lemon juice if desired; serve.