Fill a large pot with lightly salted water and bring to a rolling boil. Stir in fettuccine; cook at a boil until tender yet firm to the bite, about 8 minutes. Drain.
Melt butter in a large skillet over medium heat. Cook and stir sun-dried tomatoes, parsley, garlic, and basil in the hot butter until browned, about 5 minutes. Add scallops in a single layer; cook until they release from the bottom of the skillet, 2 to 3 minutes per side. Transfer to a large plate.
Cook and stir mushrooms and green onions in the same skillet until lightly browned and tender, about 5 minutes. Pour in Alfredo sauce; cook, stirring often, until heated through, 5 to 10 minutes. Return scallop mixture to the skillet; stir until coated with sauce and warmed through, 2 to 3 minutes.