Step 1

In a small bowl, whisk together soy sauce, rice wine vinegar, brown sugar, garlic, ginger, sesame oil and Sriracha, if using; set aside.

Step 2

In a large pot of boiling water, cook udon noodles according to package instructions; drain well.

Step 3

Heat olive oil in a large skillet over medium high heat. Add ground beef and onion and cook until beef has browned, about 3-5 minutes, making sure to crumble the beef as it cooks; drain excess fat.

Step 4

Stir in bell peppers and broccoli. Cook, stirring frequently, until tender, about 3-4 minutes. Stir in udon noodles and soy sauce mixture until well combined, about 2-3 minutes.

Step 5

Serve immediately, garnished with green onion, if desired.