Summer Pasta With Zucchini, Ricotta and Basil

Extra-virgin olive oil

small onion, finely diced

zucchini, sliced into 1/4-inch-thick pieces (for larger zucchini, cut in half lengthwise before slicing)

Salt and pepper

garlic cloves, minced, or 2 tablespoons chopped green garlic

basil, about 2 cups loose leaves

ziti or other dry pasta

ricotta, about 1 cup (see recipe)

crushed red pepper

Zest of 1 lemon

grated Parmesan, pecorino or a mixture, about 1 cup, plus more for serving