Prepare the protein: If using tofu or tempeh, cut into bite-sized cubes. If using mushrooms or plant-based meat, prepare according to the instructions. Optionally marinate with 1½ tsp dark soy sauce for extra flavor.
Cook the protein: Heat 1 tbsp of neutral oil in a large pan or wok over medium heat. Add your protein of choice and cook for 4-5 minutes, flipping to ensure even browning.
Sauté aromatics: In the same pan, add a little more oil if needed. Add the sliced onions and sauté for 2-3 minutes until softened. Stir in the ginger and garlic, cooking for another 1 minute until fragrant.
Add vegetables: Toss in the broccoli florets and sliced red bell pepper. Stir-fry for 3-4 minutes until the vegetables are bright and slightly tender. Add ¼ cup of vegetable broth (or mushroom soaking water) to help steam and soften the vegetables.
Make the sauce: In a small bowl, whisk together the soy sauce, vegetarian mushroom oyster sauce, water, sugar, Shaoxing wine, black vinegar, cornstarch, sesame oil, and sriracha (if using).
Combine and stir-fry: Return the protein to the pan, then pour the sauce over the vegetables and protein. Stir well to coat everything evenly. Cook for another 2-3 minutes until the sauce thickens and the ingredients are well combined.
Serve: Remove from heat and serve immediately over steamed rice or noodles for a complete meal. Enjoy your plant-based "beef" and broccoli stir-fry!