Heat 1 tablespoon of canola oil in a large skillet over medium-high heat. Add the cubed tofu, and cook until lightly browned on all sides, about 10 minutes; remove from the skillet and set aside. Reduce the heat to medium, and pour in the remaining canola oil. Stir in the onion, garlic, and green pepper. Cook and stir until the onion has softened and turned translucent, about 5 minutes.