Preheat oven to 375°F (190°C). Lightly oil a 9x13-inch baking dish.
Cook aromatics: Heat olive oil in a large skillet over medium heat. Add onion and garlic; sauté until softened.
Brown meat: Add ground meat, breaking it up as it cooks. Season lightly with salt and pepper.
Mix sauce: Stir in marinara sauce, gochujang, kimchi, and reserved kimchi juice. Simmer for 5–7 minutes.
Prepare cheese layer: In a bowl, mix ricotta with ¼ cup Parmesan.
Assemble:
Spread a thin layer of meat sauce on the bottom.
Add lasagna sheets.
Spread ricotta mix, then meat sauce, then mozzarella.
Repeat layers, finishing with mozzarella and remaining Parmesan.
Bake: Cover loosely with foil and bake 25 minutes. Remove foil and bake 10 minutes more until cheese is golden and bubbling.
Rest & serve: Let sit 5–10 minutes before slicing. Garnish with parsley or green onions.