Radicchio Salad with Frisée and Apples

1 head radicchio, thinly sliced Ask a question about this ingredient

1/2 head frisee, sliced Ask a question about this ingredient

1 apple, cut into matchsticks (I used Braeburn) Ask a question about this ingredient

olive oil , to taste Ask a question about this ingredient

balsamic vinegar, to taste Ask a question about this ingredient

1/2 cup walnuts, toasted Ask a question about this ingredient