Prep Ingredients: Gather and prepare all your ingredients. Thinly slice beef and any substitutes, cut carrots and onions into strips, chop green onions, and rinse spinach.

Cook Noodles: Boil water in a large pot with olive oil, add the noodles, and cook for 5-6 minutes until tender yet chewy. Drain and rinse under cold water.

Cook Beef: In a preheated skillet over high heat, sauté sliced beef in olive oil for 2-3 minutes. Add half of the soy sauce, sesame oil, and brown sugar. Remove beef and set aside.

Sauté Vegetables: In the same skillet, cook carrots and onions in olive oil for 3-4 minutes. Stir in remaining soy sauce, sesame oil, brown sugar, garlic, and green onions. Sauté another minute.

Combine: Add spinach to the skillet, turning off the heat. In a mixing bowl, combine noodles, sautéed beef, and vegetables. Toss well to coat everything in the sauce.

Serve: Dish out warm Japchae and enjoy immediately or as leftovers.