Prep the produce. Halve the tomatoes, slice the zucchini and squash thin, and slice the garlic and onion.
Keep everything bite-sized so it cooks evenly with the pasta.
Warm the pan. In a large, deep skillet or sauté pan with a lid, heat the olive oil over medium heat. Add the onion and a pinch of salt. Cook 2–3 minutes until just softened, stirring occasionally.
Sauté the aromatics. Add the garlic and red pepper flakes.
Cook 30–45 seconds until fragrant. Don’t brown the garlic—just let it bloom in the oil.
Build the base. Stir in the tomatoes and a pinch of salt. Cook 2 minutes until they start to release juices and look glossy.
Add pasta and liquid. Lay the dry pasta in the pan, breaking strands in half if needed to fit.
Pour in the vegetable broth and water. The liquid should just cover the pasta; add a splash more water if needed.
Simmer and toss. Bring to a lively simmer, then reduce heat to medium-low. Cover and cook 4 minutes, lifting the lid to stir and separate the strands once or twice so nothing sticks.
Add zucchini and squash. Stir in the sliced zucchini and squash.
Continue to cook uncovered, stirring frequently, 4–6 more minutes until the pasta is al dente and the liquid has mostly absorbed into a silky sauce. Add small splashes of water if the pan gets dry before the pasta is done.
Finish the sauce. When the pasta is just tender, remove from heat. Stir in the lemon zest, lemon juice, and Parmesan.
Toss until the cheese melts and the sauce turns glossy. Season with more salt and plenty of black pepper to taste.
Add herbs and serve. Fold in the torn basil. Divide between two bowls and top with extra Parmesan, a drizzle of olive oil, and more pepper if you like.