Fill large pot with water and place pot on stovetop over high heat. Bring water to rolling boil.
When water begins to boil, add 8 ounces flat rice noodles to pot. Boil noodles 1 minute.
After 1 minute, move pot to cool burner and let noodles soak in hot water 5 minutes.
After 5 minutes, pour noodles and water into colander. Rinse noodles under cold water and drain well. Set aside.
Add ¼ cup soy sauce, 2 tablespoons avocado oil, 5 packed tablespoons light brown sugar, 2 tablespoons rice vinegar, 1 tablespoon sriracha, and 2 tablespoons creamy peanut butter to small mixing bowl. Whisk ingredients together until fully incorporated. Set aside.
Return large pot to stovetop and set heat under pot to medium-high. Add 3 tablespoons neutral-flavored oil to pot and heat oil until shimmery.
When oil is hot, add 1 16-ounce block extra-firm tofu (cut into ½-inch cubes) to pot. Fry tofu, flipping cubes occasionally, until golden-brown on all sides. Transfer fried tofu to large bowl or plate and set aside.
Add 1 medium red bell pepper, white parts of 3 green onions, and ½ cup carrot matchsticks to pot. Stir to incorporate then sauté ingredients until softened, approximately 4 minutes.
Add 1 tablespoon fresh minced garlic and sauté, stirring constantly, until garlic is fragrant, approximately 30 to 60 seconds.
Return tofu and rice noodles to pot. Pour the prepared sauce into the pot, then add ¼ cup fresh cilantro and green parts of 3 green onions. Stir until ingredients are fully incorporated and sauce is heated through.
Portion pad thai into serving bowls. Garnish with ½ cup dry-roasted peanuts and ¼ cup fresh cilantro if desired. Serve warm with lime wedges and 1 cup fresh bean sprouts.