In a large nonstick pan, melt the butter over medium-high heat. Add the onions and celery and cook for 5-6 minutes until softened. Transfer to a large bowl.
To the bowl, add the imitation crab, sour cream, mayonnaise, soy sauce, Worcestershire sauce, Old Bay seasoning, and ½ cup of the mozzarella cheese. Mix well, then transfer to a 2 qt casserole dish.
Top with the remaining mozzarella and cheddar cheese.
Bake for 30-35 minutes until the cheese is lightly browned and the sides are bubbly. Enjoy!