Prep: 1. Thinly slice beef. 2. Roughly chop spinach. Make: 1. In a small bowl, mix the broth, soy sauce, vinegar, water, sesame oil, chili flakes, sugar (if using) and garlic. 2. Remove 1/3 cup mixture to a large bowl (reserve extra sauce); add beef and toss to coat. Marinate at room temperature 10 minutes. 3. Meanwhile, boil water for pasta and cook spaghetti according to package directions. 4. When beef is marinaded, heat 1 1/2 teaspoons olive oil over medium heat. Add the beef mixture; stir-fry 1-2 minutes or until no longer pink. Depending on the size of your skillet you may need to do two batches. 5. Toss in spinach and remaining sauce mixture; cook until spinach is wilted. 6. Drain spaghetti; add to beef mixture and toss to combine.
We love to throw in additional veggies in to make this a one pot meal. Try shredded carrots, red peppers, and snap peas!