Cook the whole wheat spaghetti or chosen noodles in a large pot of salted boiling water until al dente, about 8-10 minutes. Drain and set aside.
In a large skillet, heat olive oil over medium heat. Add minced garlic and red pepper flakes, sauté for about 1 minute until fragrant.
Add cooked chicken or tofu, broccoli florets, and sliced bell peppers to the skillet. Stir-fry for about 5-7 minutes until vegetables are tender-crisp.
Pour in soy sauce and sesame oil, stirring to combine. Add cooked noodles and toss gently to coat with the sauce. Heat through for another 2-3 minutes.
Season with salt and pepper to taste. Stir in chopped green onions and sprinkle with sesame seeds if desired. Serve hot.