Prep the chicken: Cut the chicken thighs into bite sized pieces. Season with salt and pepper, then toss with 1 tablespoon cornstarch until evenly coated.
Cook the noodles: Prepare the udon noodles according to package instructions. Drain and set aside.
Make the sauce: In a small bowl whisk together dark soy sauce, honey, sriracha, garlic, ginger, water, and 1 tablespoon cornstarch until smooth.
Brown the chicken: Heat 1 tablespoon sesame oil in a large wok or skillet over medium high heat. Add the chicken in a single layer and cook 2 to 3 minutes per side until golden and cooked through. Remove from pan and set aside.
Cook the vegetables: Add more oil if needed, then add carrots and broccoli. Cook 2 to 3 minutes. Add zucchini and cook 2-3 additional minute until crisp tender.
Combine: Return the chicken to the pan and add the green onions and cooked udon noodles.
Add sauce: Pour the sauce over everything and toss continuously for 2 to 3 minutes until thickened and glossy and evenly coated.
Serve: Divide into 4 servings and enjoy immediately.