Using a vegetable peeler (Y-peelers work best) or a mandoline, shave zucchini into long, thin ribbons. Toss zucchini slices or ribbons with 1/4 teaspoon salt in a large colander set over a bowl and let drain 15-20 minutes, until it has become more dense and moisture has been pulled out. Toss zucchini every few minutes. Pat zucchini slices dry with a kitchen towel if they are very wet.
For the croutons: Heat a large saute pan to medium heat. Add the bread and drizzle the oil, while mixing. Continue to stir the pan regularly, until the bread crumbs are golden and toasted.
In a large bowl add the zucchini, basil, 3 tablespoon of olive oil, 1-2 tablespoons of lemon juice, red onion, and 1/4 teaspoon of salt. Gently toss to combine.
Add additional garnishes: croutons, cheese, toasted nuts, fresh black pepper. Add extra oil, salt, and lemon as needed.