Bring a large pot of generously salted water to a boil. Add the pasta and stir. Once the water begins to boil vigorously again, add the 3 tomatoes and cook for 1-2 minutes until the skins split. Using a slotted spoon, transfer the tomatoes to an ice bath.
Once the tomatoes are cool enough to handle, remove the skins and core. Crush the tomatoes with your hands and transfer to a bowl until needed.
Continue cooking the pasta until al dente. Remove 3/4 cup of the pasta cooking water and set aside. Drain the pasta.
Cook the Vegetables:
While the pasta is cooking, start the sauce. In a wide pot, heat the extra virgin olive oil over medium-high until very hot. Add the scallions and cook without moving for 2-3 minutes until they begin to char. Flip and cook an additional 2 minutes.
Add the zucchini and cook in an even layer without moving for 4-5 minutes until it begins to char.
Add the garlic and cook for 45 seconds or until fragrant. Season with salt, pepper, and crushed red pepper to taste.
Prepare the Sauce:
Melt the butter into the pot of vegetables. Once frothy, add the crushed tomatoes and bring to a boil. Cook for 10 minutes until the tomatoes begin to break down and the sauce thickens.
Add the reserved pasta cooking water and parmesan cheese and bring to a boil. Boil for 5-6 minutes until thickened and reduced. Taste and season again to your preferences.
Finish the Summer Spaghetti:
Add the basil and the cooked spaghetti to the pot and toss to coat. Turn off the heat.
To Serve:
Divide the cooked summer spaghetti between shallow bowls and garnish with more basil and parmesan cheese, if desired. Enjoy!