Step 1

Heat the oil in a medium skillet over medium-low heat. Add the panko and cook, stirring and shaking the pan often, until the crumbs are spotty brown and have darkened to the color of peanut butter, 3 to 5 minutes. Transfer to a heatproof bowl or container, stir in the za'tar and the salt, and let cool completely.

Step 2

Bring 4 quarts of water and 2 tablespoons of the salt to a boil in a large pot.

Step 3

Heat the oil in a Dutch oven (or second large pot) over medium- high heat until shimmering but notsmoking. Add the zucchini and cook undisturbed until the slices on the bottom are browned on one side,5 to 7 minutes. Sprinkle with 1 teaspoon of the salt, stir gently, and continue to cook, stirring often, until most of the zucchini is softened and slightly translucent and about a third is well browned, 8 to12 minutes.

Step 4

Use a slotted spoon to transfer one- third of the zucchini to a blender (or immersion blender) and set aside. Move the remaining zucchini to one side of the pot, add the garlic and red pepper flakes to the empty space, and cook until the garlic starts to color, about 1 minute. Stir, then remove the pot from the heat. (At this point the mixture can sit, covered, for up to 2 hours.)

Step 5

Add the pasta to the boiling water and cook for 1 minute less than the low end of the package instructions. Reserve 2 cups of the pasta cooking water, then drain the pasta. Immediately return the pasta to the empty pot, cover, and set aside. Add 1 cup of the pasta water, the lemon zest and juice, and the remaining 1 teaspoon of salt to the blender with the zucchini. Start blending on low, gradually increasing the speed to high. With the blender running, add the butter and blend until smooth, 30 to 45 seconds.

Step 6

Return the pot with the sliced zucchini to medium heat and cook until it’s beginning to sizzle, about 1 minute. Add the pureed zucchini mixture and the pasta and toss until the sauce clings to the pasta,1 to 3 minutes. (If the sauce seems too thick, add more pasta water 2 tablespoons at a time until it’s the consistency of heavy cream and pools slightly in the bottom of the pot.) Remove the pot from the heat and gently stir in the feta, leaving the big crumbles intact.

Step 7

Transfer the pasta to a serving dish or individual bowls, sprinkle with some pangrattato and flaky sea salt, if desired, and serve with additional red pepper flakes and more pangrattato.