Preheat the oven to 400ºF. Line a baking sheet with parchment for easy cleanup and set aside.
Add the meatball ingredients to a large bowl and mix until just combined. Roll into 30 to 36 meatballs (I used a cookie scoop to size them evenly) and arrange on the lined baking sheet.
Transfer to the oven and bake for 15 to 20 minutes, or until cooked through.
While the meatballs cook, add the sauce ingredients to a medium saucepan and bring to a low boil. Reduce to a simmer, and cook until reduced by about 1/3 and thickened to your liking, stirring often. If using a thinner balsamic (and you want to speed up the thickening time), add the arrowroot and water slurry, whisking into the sauce and heating until thick.
Add the broccoli and water to a large saucepan and bring the water to a boil. Cover and steam until broccoli is bright green and fork tender. Drain & season with salt and pepper to taste.
Arrange the broccoli and meatballs in a large dish and coat with sauce. Serve hot, garnished with sliced green onion and toasted sesame seeds. Enjoy!