Cook pasta according to package instructions, or until al dente. Drain and rinse in cold water until completely cool. Add 2 tbsp. olive oil and lemon juice, then add salt and pepper to taste (do not under-salt). Toss to combine.
Heat remaining 1 tbsp. olive oil to medium in a stovetop pan, and add zucchini. Salt and pepper lightly, cooking and stirring for 5 minutes. Add to the pasta along with the tomatoes, scallions and parmesan, and toss to combine. Add more of what you think it needs; I like to go heavy on the Parmesan! Squeeze in a little more lemon juice, or drizzle more olive oil if it needs more moisture.
Cover and refrigerate for at least a couple of hours before serving.
Add grilled shrimp, chicken, or steak if you need a little protein.