In a small sauce pot, add light soy sauce and Japanese mirin. Grate garlic clove with a fine grater (or a microplane grater) and add to the sauce pot. In a small bowl, add cornstarch and 1/2 cup warm tap water. Stir with spoon to dissolve cornstarch into water - creating a cornstarch slurry. Add cornstarch slurry to the soy and mirin mixture. Squeeze in juice of 1/2 a lemon (straining out any seeds).
Heat pot on medium heat and stir occasionally. Sauce is done when it begins to bubble and changes from opaque to dark. Set aside.
NOTE: Mirin is a sweet cooking wine that can be purchased in most Asian supermarkets. Alternatively, you may substitute with 3 Tbsp. honey. Adjust to 3 tsp. of cornstarch if substituting with honey.
Prepare Meat & Veggies:
Broccoli: Bring a medium pot of water to boil. While waiting for the water to boil, chop broccoli to bite-sized pieces (discarding lower stem portions). Gently place broccoli pieces into boiling water and stir. Boil broccoli until it reaches a vibrant green colour (about 1 to 2 minutes). Remove from heat and strain. Set aside. NOTE: If you don't plan to use the broccoli within 30 minutes, then immerse it in ice water until ready for stir-frying. That will keep it green and crunchy longer.
Bell Peppers, Onion: De-seed and de-stem bell peppers. Chop to bite-sized pieces, diagonally. Peel both red and yellow onions. Discard the ends and chop to bite-sized pieces. Keep the yellow onions separate from the red onions. For the green onions, diagonally chop and use only the green tips. Set aside.
Bratwurst and Tofu: Cut tofu into 1/4 inch thick rectangular strips. Cut bratwurst into 1/4 inch thick circles. Set aside.
Cooking & Plating:
Bring a large wok to medium-high heat and add 2 Tbsp. canola oil. Add tofu and season with salt and pepper to taste. Sear until golden on one side. Add bratwurst and sear with tofu until golden-brown. Remove tofu and bratwurst from wok and set aside.
Bring wok back to medium-high heat and add 2 Tbsp. canola oil. Add yellow onions and a pinch of salt and cook until semi-translucent and soft.
Turn heat to high and add the following (while stirring in between each ingredient) in this order: red onions, bell peppers, broccoli, bratwurst and tofu. Once ingredients have browned evenly (without burning), turn off heat.
Add about 1/4 cup sweet & savoury sauce and toss. Garnish with chopped green onions. Serve with steamed rice.