Bring a pot of water to a boil and cook the udon noodles according to package instructions, then drain and set aside.
In a small bowl, mix soy sauce, chili garlic paste, sesame oil, brown sugar or honey, and rice vinegar until well combined.
Heat vegetable oil in a pan over medium heat and sauté the garlic and ginger until fragrant.
Add the bell peppers and cook for two to three minutes until slightly tender, then add the spinach or bok choy and let it wilt.
Add the cooked udon noodles to the pan and pour in the prepared sauce, tossing well to coat the noodles evenly.
Cook for one to two minutes until everything is heated through, then remove from heat and garnish with green onions and sesame seeds.
