Place a wok or a large nonstick saute pan over medium-high heat. Add the sesame oil and heat until shimmering, about 30 seconds. Add ginger and garlic and stir for a few seconds. Add the fish and cook for 2-4 minutes, depending on the variety you’re using, until the fish is just cooked. Spoon the fish out of the pan and onto a side plate, then add the broccoli or snow peas, to the pan. Stir-fry for 1 minute to give some color, then add the stock, and the soy sauce. Stir to combine, then cook for 1-2 minutes more, or until the vegetables are crisp-tender. Add the fish back into the pan and stir to combine.
Remove from the heat. Garnish with black pepper or red pepper flakes, if using. Serve the fish stir-fry immediately with steamed rice.