Halve the zucchini lengthwise, then cut each piece into thirds on a diagonal. Cut a crosshatch pattern into the flesh side of each piece, cutting about ⅛-inch deep (this will help the seasonings penetrate the zucchini later). Sprinkle the crosshatched side with salt and pepper.

Heat the oil in a large cast-iron skillet over medium-high heat. When the oil is shimmering, add all the zucchini, cut-side down, in a single layer (if it doesn’t all fit, cook it in two batches). Season the top-facing side with more salt and pepper.

Cook the zucchini, undisturbed, until it is deeply browned, 4 to 6 minutes. Carefully flip with tongs and brown the other side for another 5 minutes. Remove the zucchini from the skillet and set aside. Take the skillet off the stove for at least 1 minute so it can cool a bit.

Return the skillet to medium-low heat. Add the butter and garlic and cook until fragrant, about 30 seconds. Add the wine and deglaze the pan (scrape up the browned bits from the bottom of the pan with a wooden spatula). Simmer to evaporate the alcohol, about 1 minute.

Add the broth and lemon juice to the pan, then add the zucchini back, crosshatched-side up. Baste the zucchini with the liquid and bring to a simmer. Cook until most of the liquid has evaporated and the zucchini is tender, 10 to 12 minutes.

Scatter the capers and parsley on top. Serve warm or at room temperature.