Finely grate the zest of the lemons and toss it into a large serving bowl. Squeeze the juice into a cup (you want a scant ½ cup) and hold on to the lemon halves. Cut the squash into quarters the long way, then cut each piece crosswise into ¼-inch slices (they'll be wedge-shaped). Fill a large pot with generously salted water, toss in the lemon halves, and bring to a boil. Add the pasta and cook­ according to the package directions until al dente.

As the pasta bubbles away, pour ¼ cup of the oil into a large skillet set over medium-high heat. Add the shrimp (do this in batches if you think the pan will be crowded), season with salt, pepper, and a pinch of cayenne and cook for about 3 minutes, turning once, until the shrimp are pink; you want them to stay tender, so taste them as soon as they turn color. Using a slotted spoon, transfer the shrimp to a bowl.

Add another 2 tablespoons oil to the skillet and, when it's hot, toss in the squash (again, working in batches if necessary). Season with salt and pepper and cook over high heat, turning as needed, until the squash is lightly golden, 3 to 5 minutes. With a slotted spoon, transfer to the bowl with the shrimp. When the pasta is cooked, scoop out ½ cup of the cooking liquid and set it aside, then drain the pasta.

Return the skillet to medium-high heat, add the remaining 2 tablespoons oil and the pasta, and toss the pasta around in the oil until it’s coated. Add the shrimp and squash, the reserved pasta water, the lemon juice and butter, stir to blend, taste for salt, pepper, and cayenne, and cook for just a minute or two—the sauce will thicken slightly and the pasta will have a nice shine.

Stir in the tomatoes and whatever juices there are. Turn everything out into the serving bowl with the zest, top with the herbs, and stir to mix. Serve immediately.