If your nuts aren’t pre-roasted, start by toasting those first. Preheat your oven to 350ºF/175ºC and spread the nuts out on a sheet pan. Roast pistachios for 8 to 10 minutes, or almonds for 10 to 15 minutes. Or, you can toast them in a frying pan for 3 to 5 minutes, tossing frequently (though they toast less evenly this way).
Make the chili oil. Add the chili flakes and olive oil to a small saucepan. Turn the heat to low. Once it’s at the most gentle simmer (tiny slow, barely-there bubbles), simmer for 5 minutes. Remove from the heat and pour into a bowl or jar to stop cooking.Tip: If you have an electric stove, pay close attention because it may burn if you don't pay attention to it. Trim the ends and tops of the zucchini. Slice the zucchini using one of these methods (see Note 4). Transfer sliced/chopped zucchini to a large bowl.Option 1: For ½” pieces, slice the zucchini in half, lengthwise. Then slice both halves in half, lengthwise, so you have four quarters. If zucchini is fat, slice again so you have eighths. From there, slice the zucchini into ½” (~1 cm) pieces.Option 2: For skinny batons, cut the zucchini crosswise into 2-inch pieces. Slice each piece in half, lengthwise, then into ¼”-thick slabs (.5 cm thick). Now slice those slabs into ¼”-thick batons. Make the herby pistachio topping. Chop the pistachios. Stack the leaves of basil and roll them up like a cigar, then finely sliver the leaves (i.e., chiffonade). Do the same for the mint. For any small leaves, you can tear them with your hands.
In a bowl, combine the basil, mint, chopped pistachios, lemon zest, and a few pinches of flaky salt and a generous amount of pepper. Mix together to combine. Slice the zested lemon in half and set aside for the next step.
Assemble. Drizzle the zucchini with about 2 tablespoons of the chili oil. Squeeze on about ½ tablespoon lemon juice, and gently toss with a spatula. Add the herby pistachio topping and feta, and toss to combine. Taste, adding flaky salt or pepper to taste, or more chili oil for richness or lemon juice for tang. Store leftover chili oil in a jar in the fridge. It will last several weeks, though you may need to briefly leave it out at room temp to return the oil to its liquid state.