In a skillet over medium heat, melt the unsalted butter. Add the chopped onion and sauté until tender, about 3-4 minutes.
Stir in the baked beans and the sliced turkey hot dogs. Mix in the brown sugar, ketchup, yellow mustard, and celery salt until everything is well combined.
Transfer the mixture to an oven-safe casserole dish. If using, sprinkle bacon bits on top. Bake for 25-30 minutes, stirring halfway through to ensure even heating.