Pat tofu dry and cut into 1/2-inch cubes. Combine with half of the five-spice powder in a medium bowl.
Heat the canola oil in a large nonstick skillet over medium-high heat. Add tofu and cook, stirring every 1 to 2 minutes, until golden brown, 7 to 9 minutes total. Tranfer to a plate.
Meanwhile, wisk water, oyster sauce, cornstarch and the remaining five-spice powder in a small bowl.
Add broccoli, yellow and red bell pepper to the pan and cook, stirring occasionally until beginning to soften, about 4 minutes. Add ginger and garlic and cook, stirring, until fragrant, about 30 seconds. Return the tofu to the pan along with the peanuts and stir to coat with sauce; stir in hot sesame oil (if using).