Press the tofu for at least 15 minutes to remove excess moisture, then cut into cubes.

In a large skillet over medium heat, sauté the diced onion and minced garlic until fragrant, about 4-5 minutes. Add the diced carrots and cook while you prepare the sauce.

In a small bowl, whisk together the gochujang, boiling water, soy sauce, rice vinegar, sriracha, and red chili flakes (if using) until smooth.

Add the tofu cubes and remaining vegetables (broccoli and red bell pepper) to the pan. Pour in the sauce and stir to combine, making sure everything is evenly coated.

Cook until the vegetables are tender-crisp, about 5 minutes. Toss with sesame oil to taste and remove from heat. Serve immediately over steamed rice.