Extra-virgin olive oil
1 small onion, finely diced
2 pounds zucchini, sliced into 1/4-inch-thick pieces (for larger zucchini, cut in half lengthwise before slicing)
Salt and pepper
2 garlic cloves, minced, or 2 tablespoons chopped green garlic
1 ounce basil, about 2 cups loose leaves
1 pound ziti or other dry pasta
8 ounces ricotta, about 1 cup
Pinch of crushed red pepper
Zest of 1 lemon
2 ounces grated Parmesan, about 1 cup, plus more for serving
Put a pot of water on to boil. In a large skillet over medium-high heat, cook the onions in 3 tablespoons olive oil until softened, 5 to 8 minutes. Reduce heat if needed to keep onions from browning. Add zucchini, season with salt and pepper, and continue cooking, stirring occasionally until soft, about 10 minutes. Turn off heat.
Meanwhile, use a mortar and pestle to pound garlic, basil and a little salt into a rough paste (or use a mini food processor or microplane). Stir in 3 tablespoons olive oil.
Salt the pasta water well before adding pasta. Boil per package instructions but make sure to keep pasta al dente. Drain, reserving 1 cup of cooking water.
Add cooked pasta to zucchini in skillet and turn heat to medium-high. Add 1/2 cup cooking water, then the ricotta, crushed red pepper and lemon zest, stirring to distribute. Check seasoning and adjust. Cook for 1 minute more. Mixture should look creamy. Add a little more pasta water if necessary. Add the basil paste and half the grated cheese and stir to incorporate. Sprinkle with additional cheese before serving. Serve immediately.