Prep everything first. Slice the garlic, chop the veggies, and have the stock measured and ready.
This cooks quickly once it starts.
Warm the pan. Set a large, deep skillet or Dutch oven over medium heat. Add 1 tbsp olive oil and 2 tbsp butter. When the butter melts and foams, add the garlic.
Bloom the garlic. Cook the garlic for 30–60 seconds until fragrant and just turning golden at the edges. Don’t let it brown deeply or it will taste bitter.
Build the base. Add the broccoli, zucchini, and bell pepper with a pinch of salt.
Toss to coat in the garlic butter and sauté 2–3 minutes to soften slightly.
Add pasta and liquid. Lay the pasta in the pan (break long noodles in half if needed). Pour in 3 1/2 cups stock or water. Add another 1 tbsp olive oil, a pinch of red pepper flakes, and a few grinds of black pepper.
Simmer and stir. Bring to a gentle boil, then reduce to a lively simmer.
Cook uncovered, stirring and tongs-tossing frequently so pasta doesn’t stick. Stirring releases starch and helps the sauce become silky.
Add quick-cooking veggies. At around the 6–8 minute mark (depending on pasta shape), add cherry tomatoes. Keep stirring as the liquid reduces.
Finish the cook. When the pasta is just shy of al dente and there’s still some starchy liquid in the pan, add the spinach to wilt. If the liquid runs low before pasta is tender, add splashes of stock or water.
Create the sauce. Lower the heat.
Stir in remaining 2 tbsp butter, the lemon zest, and 1–2 tsp lemon juice. Sprinkle in Parmesan gradually, tossing until it melts into a glossy sauce. Adjust salt and pepper to taste.
Rest and garnish. Turn off heat and let the pasta sit 1 minute to thicken. Top with chopped parsley or basil and extra Parmesan.
Serve warm with lemon wedges on the side.