First, prepare Bulgogi. In bowl of food processor, combine pears, onion, garlic, ginger root, soy sauce, rice wine vinegar, sesame oil, brown sugar, Korean chile flakes and salt; process until smooth. Place ribeye in shallow dish; pour marinade over top and cover. Refrigerate at least 3 hours or overnight. Remove meat from marinade. Preheat grill to high heat; grill meat to desired doneness.
Cook pasta according to package directions to al dente; drain and set aside. Preheat oven to 350˚F.
In sauce pan, melt butter over medium heat; stir in flour. Cook 3 minutes until flour lightly browns. Whisk in milk slowly and bring to simmer, whisking constantly to avoid burning. Simmer until mixture thickens slightly, remove from heat and cool slightly. Add cheese and stir until cheese is mostly melted. Add cooked pasta to cheese mixture; mix well. Add Bulgogi and kimchi and mix. Pour mixture into 9x12-inch baking dish and bake 30 minutes. Garnish with additional kimchi before serving, if desired.