How to Make It
Combine vinegar, sugar, 1½ teaspoons salt, and several grinds of pepper in a small saucepan. Bring to a boil; add half of the shallots and stir to coat them in the liquid. Remove from heat and set aside until softened, about 10 minutes.
Toss cucumbers, dill, and pickled shallots with the pickling liquid in a large bowl. Season to taste and set aside.
Combine oil and remaining half of shallots in a small saucepan. Place over medium heat and cook, swirling occasionally, until shallots are golden brown, 8 to 10 minutes. Remove from heat and, using a slotted spoon, transfer fried shallots to a paper towel–lined plate; season with a pinch of salt. Reserve 3 tablespoons of the frying oil.
Toss cucumber mixture with reserved oil and top with fried shallots.