Preheat oven to 425°F. Combine onion, mushrooms, and 2 tbsp vegetable oil on foil-lined baking sheet and toss to coat. Roast until mushrooms are browned and onions are soft, 20 to 25 minutes, stirring halfway through.

Meanwhile, wrap tortillas in foil and place in oven until heated through, 5 to 6 minutes.

Combine sugar, tamari, just half the ginger, just 1 tsp sesame oil, 1 tbsp water, ¼ tsp salt, and a pinch of pepper in small bowl and whisk to dissolve sugar. Add to cooked mushrooms and onions, toss to combine, and return to oven. Continue to roast until sticky, 3 to 4 minutes.

Divide warm tortillas between plates. Top with mushroom bulgogi, kimchi, and cilantro. Serve tacos with extra kimchi. 잘 먹겠습니다!

For 4-serving meal, double all ingredients. You may need to cook in batches, in larger cooking vessels, or for longer cook times. Follow visual cues in 2-serving recipe.