Bring a large pot of salted water to a rolling boil. Add the spaghetti and cook until al dente, about 8-10 minutes. Reserve 1/2 cup of pasta water before draining.

In a large skillet, heat 2 tablespoons of vegetable oil over medium heat. Add the minced garlic and chopped onion. Sauté for about 3-4 minutes until translucent.

Stir in the gochujang, soy sauce, honey, and rice vinegar. Let it simmer for 2 minutes until the sauce thickens.

Add the mixed vegetables and cook for an additional 3-4 minutes until they're tender-crisp.

Pour in the reserved pasta water, stirring to create a smooth sauce. Allow to simmer for 1 minute.

Add the drained spaghetti and toss to coat with the sauce and vegetables. Cook for another minute to soak up flavors.

Stir in the sliced green onions and sesame seeds, cooking for another minute. Adjust seasoning with salt and pepper.

Serve the pasta immediately, garnished with cilantro or parsley if desired.