Preheat oven to 375 degrees. Drizzle oil into a large pot of boiling water. Add pasta and cook for 6 to 8 minutes. Drain well.
In the meantime make a rue with the butter, flour , add milk to make white sauce. Remove from heat and stir in Gruyere, Cheddar, 1 tablespoon salt and the pepper, and nutmeg. Add the cooked macaroni and lobster and stir well.
Place in 6 to 8 individual gratin dishes or large casserole dish. Melt the remaining 2 tablespoons butter, combine with fresh bread crumbs, and sprinkle on top of the casserole.
Bake 30 to 35 minutes or until sauce is bubbly and the bread crumbs have browned.