Simply make a basic white sauce & add whatever cheese you like to taste. Add your cooked seafood - shrimp, scallops, seafood mix - to HALF the sauce & fill & roll your flour tortillas, placing them seam-side down in a baking dish.
Mix the remaining half of the white sauce with a small can of green enchilada sauce, pour over the top of the enchiladas, top with more grated cheese, & bake until cheese has melted & everything is heated through.
Top with chopped cilantro & serve.