Heat the sesame oil in a medium saucepan over medium heat. Add the fish and cook, stirring frequently, for 2-3 minutes.
Add the garlic, ginger, scallions, and broccoli. Continue to cook, stirring frequently, for another 2-3 minutes.
Add the water, tamari, and vinegar to the pot. Cover and simmer for 5-6 minutes. Turn off the heat, stir in spinach, and let sit for a few minutes. Remove from the heat, season with pepper to taste and serve.