In a small bowl, mix the cornstarch with cold water until smooth. Set aside.
Heat 1 tablespoon of oil in a large skillet over medium-high heat. Add ground beef and cook until browned. Remove and set aside.
In the same skillet, add the remaining oil, ginger, garlic, and red bell pepper. Sauté for about 2 minutes.
Add broccoli florets and stir-fry for another 3 minutes. Return beef to the skillet.
Pour in sweet chili sauce and soy sauce, adding the cornstarch mixture. Stir until the sauce thickens and evenly coats the beef and vegetables.
Remove from heat, garnish with green onions, and serve immediately.