Boil the pasta: Bring a large pot of salted water to a boil. Cook the pasta until just shy of al dente.
Reserve 1 cup of pasta water, then drain.
Prep the veggies: While the water heats, slice and chop all vegetables so they’re ready to go. Aim for bite-size pieces for even cooking.
Sauté aromatics: In a large skillet, heat olive oil over medium. Add the onion and a pinch of salt.
Cook 3–4 minutes until softened. Stir in the garlic and red pepper flakes; cook 30 seconds until fragrant.
Add sturdy vegetables: Add broccoli and asparagus with a splash of pasta water (2–3 tablespoons). Cook 3 minutes, stirring, until bright green and just tender.
Add quick-cooking vegetables: Stir in zucchini, yellow squash, and cherry tomatoes.
Cook 3–4 minutes until the squash is crisp-tender and tomatoes are slightly burst.
Finish the sauce: Reduce heat to low. Add butter, lemon zest, and lemon juice. Stir until the butter melts and everything looks glossy.
Add peas and warm through for 1 minute.
Toss with pasta: Add the drained pasta to the skillet. Sprinkle in Parmesan and half the basil. Add 1/3 to 1/2 cup reserved pasta water, tossing until the sauce clings.
Season generously with salt and black pepper.
Adjust and serve: Taste and add more lemon, cheese, or pasta water if needed. Top with remaining basil and extra Parmesan. Serve warm.