Heat a skillet over medium-high. Add sesame oil, then sauté the onion until it’s soft and a touch translucent, about 3–4 minutes.
Add garlic and ginger; stir for about 30 seconds until fragrant. Don’t let them burn—nobody wants bitter garlic.
Push the veggies aside and crumble in the ground beef. Cook, breaking it up, until it’s browned and no longer pink, about 5–7 minutes.
Stir in soy sauce, gochujang, and brown sugar. Mix well so every bit of beef gets that glossy, spicy coating.
Pour in water or broth and simmer 2–3 minutes to let the flavors meld. If the sauce gets too thick, splash in a little more liquid.
Taste and adjust. If you want more sweetness, add a touch more brown sugar; for more heat, add chili flakes a pinch at a time.
Remove from heat. Scatter green onions and sesame seeds on top. Serve hot and pretend you planned this all along.