Add the garlic, red pepper flakes, sambal and Fresno chiles to the beef and cook until fragrant, about 2 minutes. Add shallot and smashed 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 vinegars, water, soy sauce, and sugar. Reduce heat to medium and cook, stirring, until sauce is reduced slightly, about 3-4 minutes. Season with salt and pepper to taste.