Korean Fried Chicken Sauce

Whisk ketchup, green onion, garlic, lemon juice, honey, chile-garlic sauce, red pepper flakes, and black pepper together in a saucepan over medium-high heat; add enough water to reach desired sauce consistency. Bring sauce to a simmer; reduce heat to medium-low, and simmer until thick and flavors blend, about 5 minutes. Cool to room temperature and season with salt.