Preheat the oven to 450 degrees F and line a baking sheet with foil. Halve 2 zucchini lengthwise; scoop out the seeds, leaving a 1/4-inch-thick shell. Chop the scooped-out zucchini flesh and transfer to a bowl. Grate the remaining whole zucchini on the large holes of a box grater; add to the bowl along with 1 teaspoon salt. Set aside 10 minutes, then squeeze out the liquid.
Heat the olive oil in a skillet over medium-high heat. Add the garlic, minced jalapeno, chile powder and grated zucchini mixture; cook until tender, 4 minutes. Let cool, then stir in the cheese. Spoon into the zucchini halves. Transfer to the baking sheet and bake until bubbling, 20 minutes.
Combine the tomato, scallions and cilantro in a small bowl. Spoon over the zucchini, then top with pickled jalapenos.