Bring a large pot of well-salted water to a boil. It should taste like the sea. Cook the penne according to the package directions until al dente. Before you drain it, scoop out about a quarter cup of the starchy pasta water and set it aside. Drain the pasta and set it aside.

While the water heats, warm the olive oil in a large deep skillet over medium heat. Add the sliced garlic and red pepper flakes at the same time. Cook for about 2 minutes, stirring constantly, until the garlic is golden and very fragrant. Watch it closely because garlic goes from golden to burnt quickly.

Add the sliced zucchini and salt to the skillet. Stir to coat the zucchini in the oil and cook for 3 to 4 minutes, turning the pieces occasionally, until the edges start to look slightly golden and the zucchini is just beginning to soften. You want it to hold its shape in the final dish.

Pour in the crushed tomatoes and stir everything together. Raise the heat to medium-high until the sauce starts bubbling, then reduce back to medium and simmer for 10 minutes, stirring occasionally. The sauce will deepen in color and thicken slightly. Taste it now and add more red pepper flakes if you want more heat, and the optional pinch of sugar if the tomatoes taste sharp. Season with salt.

Add the drained penne to the skillet and toss to coat every piece in the sauce. If the sauce looks too thick or the pasta seems dry, splash in some of the reserved pasta water a tablespoon at a time and toss until the consistency is glossy and clingy, not watery.

Remove from heat, scatter the fresh parsley over the top, and toss once more. Serve immediately. Pass extra red pepper flakes at the table for anyone who wants more heat.