Prepare the udon noodles according to the instructions on the package. Set aside.
Wash the vegetables and cut the red bell pepper, the shiitake mushrooms, and the pak choi into thin strips. Divide the broccoli into small florets.
Cut the tofu into cubes. In a small bowl add two teaspoons of soy sauce and 1/3 cup of corn starch. Make sure all of the tofu cubes are covered.
Heat some sesame oil in a large pan and pan-fry the tofu cubes for about 5 minutes on high heat or until they're golden and crispy. Set aside.
In the same pan, heat some more sesame oil and sauté the shallots for about 3 minutes or until they're translucent. Then add the red bell pepper, the shiitake mushrooms, the broccoli, and the pak choi. Cook for about 8 minutes until the vegetables are tender.
Then add the cooked udon noodles.
Make the sauce. In a small bowl, combine the soy sauce, the Worcestershire sauce, the brown sugar, the mirin, and the cayenne pepper.
Add the sauce to the vegetables and the udon noodles together with the tofu and stir well. Cook for another 2 minutes or until heated through. Sprinkle some sesame seeds and chopped green onions on top. Serve immediately.