Preheat oven to 450°F. Line baking sheet with foil or parchment paper.
Combine ground beef, green onions, ginger, garlic, salt, and pepper in bowl. Mix gently until just combined.
Roll into tablespoon-size balls and place on one side of prepared baking sheet.
Add broccoli to other side of baking sheet. Toss with olive oil, salt, and pepper.
Bake 15-18 minutes until meatballs reach 160°F internal temperature and broccoli is tender-crisp with charred edges.
While baking, combine vegetable oil, soy sauce, brown sugar, garlic, ginger, water, vinegar, and red pepper flakes in skillet. Bring to simmer over medium-high heat and cook 8-10 minutes.
Whisk cornstarch with cold water until smooth. Pour into simmering sauce while stirring constantly. Cook 2-3 minutes until thickened and glossy.
Remove from heat. Add cooked meatballs to sauce and toss until completely coated.
Serve meatballs and sauce over rice, topped with broccoli, green onions, and sesame seeds.
Notes
Use 80/20 ground beef for juiciest meatballs. Don’t overmix meat or meatballs will be tough.
Low-sodium soy sauce prevents overly salty sauce. Taste before adding extra salt.
Meatballs freeze well without sauce for up to 3 months. Make fresh sauce when reheating.