I am not sure if I got it right but maybe this is what you are looking for?
scala> val a: List[List[(List[String], Double)]] = List(List((List("foo asd", "asd foo"), 2.6)))
scala> a map (_ map { case (k, v) => (k map (_.replaceAll("foo", "goo")), v) })
res1: List[List[(List[String], Double)]] = List(List((List(goo asd, asd goo),2.6)))
Edit
to answer the comment let me first remove spaces and use dots
scala> a.map(_.map { case (k, v) => (k.map(_.replaceAll("foo", "goo")), v) })
and now, expand _.method(param) to x => x.method(param)
scala> a.map(b => b.map { case (k, v) => (k.map(c => c.replaceAll("foo", "goo")), v) })
You have 3 levels of nested lists, and one is inside a tuple, it won't be pretty, you need to map over each of them and extract last one from tuple.