Cook the spaghetti in a pot of boiling salted water following the package directions. Add 1 teaspoon of kosher salt for each quart of water.

While the pasta is cooking, heat the vegetable oil in a small skillet over medium heat. Add the green onions, garlic, and chili crisp. Cook, stirring, until the mixture is aromatic, about 1 to 2 minutes.

Transfer the green onion mixture to a small bowl and let it cool slightly. Add the brown sugar, soy sauce, oyster sauce, and sesame oil.

Drain the spaghetti and transfer it to a serving bowl. Add the garlic sauce mixture and toss to blend thoroughly.

Garnish with green onion tops and serve hot.