Como dizer "macarrão ao molho" em inglês

What kind of "molho"?
There are plenty of kinds, even because pasta is associated with Italian food and they are inventinve with the names of food (both pastas and sauces, gravies, what you have.)
So, to mention some few examples:
Pasta al sugo = Macarrão ao sugo -
Sugo being a sauce - some chefs, cough! Cough! Granted, not all chefs, there´s a polimic about how word to define it (sugo) a gravy or a sauce.
So, other way to say that would be "pasta with sugo sauce". I am leaving out other ingredients that would come to the plate in a restaurant, because I am focusing in the pair "macarrão" - "molho" here.

Pasta al Pesto = Macarrão ao molho Pesto.
Fettuccine with Pesto = Fettuccine ao molho Pesto (Fettuccine - a type of Tagliatelle, they say)
Here could be also, "Fettuccine al Pesto" (a version that seems like more close to the Italian Language and that of Chefs, etc).

To say "macarrão ao molho" in a general way, you could say "pasta with sauce on the top (any kind of thousands of sauce)/past with gravy on the top (same goes to gravies, thousands of possibilities).

Well, I am not much kitchen-savvy, others may expand and improve my answer, feel free to.