In a large nonstick skillet, heat canola oil and sauté onion, mushrooms, and tempeh until tempeh is lightly browned and onions are softened, about 4 minutes. Stir in ginger, garlic, bell pepper, carrot, and broccoli and stir-fry for 2 minutes, until broccoli turns bright green. Whisk in cornstarch mixture and cook until the mixture just begins to bubble. Season with additional toasted sesame oil and hot pepper flakes, if desired.