Cook the spaghetti according to package instructions until al dente. Drain and set aside.
In a large skillet, heat 1 tablespoon of olive oil over medium-high heat. Season the flank steak with salt and pepper, then add it to the skillet. Cook for about 3-4 minutes until browned, stirring occasionally. Remove the steak from the skillet and set aside.
In the same skillet, add the remaining tablespoon of olive oil. Add the minced garlic and red pepper flakes, sautéing for about 30 seconds until fragrant.
Stir in the soy sauce, honey, and rice vinegar. Bring the mixture to a simmer and let it cook for 2-3 minutes until slightly thickened.
Return the cooked steak to the skillet, tossing to coat it in the sauce. Add the cooked spaghetti and toss everything together until well combined.
Remove from heat and garnish with chopped green onions before serving.