Cook the rice according to package directions. Set aside.Place the tempeh cubes in a shallow glass bowl in a single layer, if possible. Whisk together the tamari, vinegar, mirin, sesame oil, sugar, garlic, ginger, and red pepper flakes in a separate small bowl. Pour over the tempeh and stir so that it gets evenly coated. Cover and let sit for 20-30 minutes.Heat the grapeseed oil in a large wok or nonstick skillet over medium heat. Place the tempeh cubes in the pan, leaving as much marinade as possible in the bowl. Cook for 7-8 minutes, until browned on all sides. Transfer to a plate while you prepare the vegetables.Heat the oil in the same skillet that you used to cook the tempeh. Add the carrots, zucchini, and broccoli to the pan. Cook, stirring frequently, for 3 minutes, or until the broccoli and carrots are starting to become tender. Reduce the heat to low and pour in the reserved marinade from the tempeh. Allow to cook for 3-5 minutes, or until the broccoli is crisp-tender.Combine all of the ingredients in a small bowl and whisk to combine. Season to taste. Store in the refrigerator for up to 1 week.Divide the rice evenly among four bowls. Top each with a quarter of the tempeh and vegetables. Sprinkle with the sesame seeds and drizzle with the sriracha mayo. Serve warm.