Bring a pot of lightly salted water to a boil and cook the linguine until al dente, according to package directions. Drain and either rinse quickly in cool water or toss with a drizzle of olive oil to prevent sticking.
While the pasta cooks, heat the oil in a nonstick 12-inch skillet over medium heat. Add the onion, garlic and red pepper flakes, if using, and cook, stirring often, until the onion turns translucent, 3-4 minutes.
Add the zucchini, tomatoes, broth and a pinch of salt and pepper. Bring the mixture to a simmer, and cook until the zucchini and tomatoes soften, 5-10 minutes; the mixture will thicken a bit as the liquid evaporates and it cooks down. Stir every once in a while to prevent sticking and moderate heat, if needed. Season to taste with additional salt and pepper, if needed.
Toss the drained pasta with the zucchini/tomato mixture. Add the basil and Parmesan cheese and toss again. Serve immediately.
