Fennel, Grapefruit, and Apple Salad

2 bulbs fennel

trimmed and thinly sliced

½ red onion

thinly sliced

1 green apple

peeled and thinly sliced

1 teaspoon lemon juice

1 red grapefruit - peeled

white pith cut off

and sectioned

2 tablespoons chopped toasted walnuts

or to taste

1 tablespoon torn basil leaves

or to taste

2 teaspoons lemon juice

or to taste

2 teaspoons lime juice

or to taste

2 teaspoons grapefruit juice

or to taste

¼ cup extra-virgin olive oil

or to taste

salt and ground black pepper to taste