Prepare the Sauce: In a small bowl, whisk together the soy sauce, rice vinegar, sesame oil, water, cornstarch, brown sugar, and crushed red pepper. Set aside.

Prepare the Tofu: Pat the tofu dry with a paper towel, then cut it into bite-sized cubes. For a crispier texture, lightly press the tofu with a weight for 15-20 minutes to remove excess moisture.

Sauté the Tofu: In a spacious skillet or wok, warm one tablespoon of vegetable oil over medium-high heat until it’s shimmering and ready for cooking. Add the cubed tofu and cook for 5-7 minutes, turning occasionally, until golden brown on all sides.

Stir-Fry the Vegetables: In the same skillet, pour in the remaining tablespoon of oil, preparing for the next steps in your cooking process. Add the sliced red onion and cook for 2 minutes until it begins to soften. Add the garlic and ginger, stirring until fragrant, about 1 minute.

Add Zucchini and Bell Pepper: Add the zucchini and red bell pepper to the skillet. Stir-fry for 3-4 minutes, until the vegetables are slightly tender but still crisp.

Combine Tofu and Sauce: Add the tofu back into the skillet alongside the vegetables. Quickly stir the sauce to combine, then drizzle it over the tofu and veggies. Toss everything together to ensure an even coating, and let it cook for another 2-3 minutes until the sauce thickens a bit.

Serve: Serve hot over steamed rice or noodles, garnished with extra crushed red pepper or sesame seeds if desired.