Step 1

Cut cucumbers crosswise into 4"-thick pieces. Using a rolling pin, meat mallet, or the flat side of a chef’s knife, lightly crush cucumbers, then slice crosswise into ½"-thick slices; set aside.

Step 2

Heat oil in a large skillet, preferably cast iron, over high. Add beef and a pinch of salt; break up meat into small pieces with a wooden spoon then spread out in pan to create a single layer. Cook, undisturbed, until bottom side is browned and crisp, about 5 minutes. Break up meat with a spatula and turn over pieces. Cook until other side is browned and crisp and meat is cooked through, 5–7 minutes.

Step 3

Push meat to one side of pan and add garlic and chiles. Cook, stirring often, until fragrant and softened, about 2 minutes. Mix garlic and chile into meat. Add shallot and reserved cucumbers and cook, tossing occasionally and scraping up any browned bits, until cucumbers are softened and translucent, about 4 minutes. Remove skillet from heat and stir in vinegar, soy sauce, and sugar. Set skillet over medium heat and cook, stirring, until sauce is reduced slightly, about 2 minutes. Season with salt and pepper.

Step 4

Spoon beef and cucumbers over rice and top with herbs. Serve with lime wedges for squeezing over.