Heat 1 tablespoon of the canola oil in a large nonstick skillet over medium-high. Add the tofu and cook until golden, about 4 minutes per side. Transfer to a bowl and reserve. Return the skillet to the heat: add the asparagus, cook 1 minute and add 2 tablespoons water. Continue to cook, tossing occasionally, until bright green, about another 1 1/2 minutes. Transfer to a small bowl. Heat 1 teaspoon of the canola oil in the skillet: add the bell pepper; cook 2 minutes and transfer to a small bowl. Heat 1 teaspoon canola and add the radishes, cook 1 minute and transfer to a small bowl. Heat the remaining 1 teaspoon oil, add the scallions and cook until slightly softened, about 2 minutes; transfer to a small bowl. Return skillet to the heat and add the spinach: cook, tossing, until wilted, 1 1/2-2 minutes.