Boil the pasta. Bring a large pot of well-salted water to a rolling boil.
Cook the pasta until just shy of al dente. Reserve 1 cup of pasta water, then drain.
Prep the vegetables while the water heats. Trim the asparagus, slice the zucchini, and halve the snap peas. Have the peas, spinach, lemon, and herbs ready to go.
Soften the aromatics. In a large skillet, warm the olive oil over medium heat. Add the shallot and a pinch of salt.
Cook 2–3 minutes until translucent, then add the garlic and a pinch of red pepper flakes. Stir for 30 seconds, just until fragrant.
Cook the sturdy veg first. Add asparagus and zucchini to the skillet with a splash of pasta water. Season with salt and pepper.
Cook 3–4 minutes, stirring, until crisp-tender.
Add quick-cooking greens. Stir in snap peas and peas. Cook 2 minutes more. Toss in the spinach and let it wilt.
Make it saucy. Add the drained pasta to the skillet.
Pour in 1/2 cup reserved pasta water, lemon zest, and lemon juice. Toss vigorously over medium heat for 1–2 minutes until everything is glossy and combined. If using, swirl in the butter.
Finish with cheese and herbs. Off the heat, sprinkle in the grated Parmesan and most of the herbs.
Toss until the cheese melts and lightly thickens the sauce. Add more pasta water if it looks dry.
Taste and adjust. Add salt, pepper, extra lemon, or red pepper flakes to taste. Drizzle with a little olive oil.
Top with remaining herbs and more cheese at the table.