Get that pasta going. Bring a large pot of generously salted water to a boil. Cook pasta according to package directions until al dente. Remember: The pasta will continue cooking slightly when you toss it with the hot vegetables, so aim for the lower end of the cooking time range. No one wants mushy pasta!
Prep your veggies. While the pasta water is coming to a boil, slice and dice all your vegetables. Having everything prepped before you start cooking will make your life so much easier. Plus, look at that rainbow of colors you've created! Instagram-worthy before it even hits the pan.
Start the sauce base. In a large skillet over medium heat, warm 2 tablespoons of olive oil. Add the onion and sauté until softened, about 3 minutes. Add the garlic and red pepper flakes (if using) and cook for another 30 seconds until fragrant. Your kitchen should be smelling pretty amazing right about now.
Cook those veggies properly! Here's where the magic happens. Add the bell pepper to the skillet and cook for 2 minutes, then add the zucchini and yellow squash and cook for just 2 more minutes. These vegetables should still have a bit of crunch! Add the cherry tomatoes and peas (if using fresh peas; if frozen, wait). Season with salt and pepper and cook for just 1 minute more.
Reserve some pasta water! Before draining the pasta, scoop out about 1/2 cup of the starchy pasta water. This liquid gold will help create a silky sauce.
Bring it all together. Drain the pasta and immediately add it to the skillet with the vegetables. If using frozen peas, add them now – they'll thaw instantly in the heat. Add the butter, remaining tablespoon of olive oil, lemon zest, lemon juice, and about 1/4 cup of the reserved pasta water. Toss everything together over low heat until well combined and a light sauce forms, adding more pasta water if needed.
Finish with freshness. Turn off the heat and fold in the fresh basil, parsley, and Parmesan cheese. Give it a taste and adjust seasonings if needed.
Serve in style. Divide among bowls and top with an extra sprinkle of Parmesan, a drizzle of good olive oil, and some black pepper. Congratulations, you just made the most colorful dinner of the week!