Combine soy sauce, rice vinegar, brown sugar, sesame oil, grated ginger, and minced garlic in a bowl. Whisk until well combined. Set aside.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add broccoli and red bell pepper, season with salt and pepper. Sauté for 3-4 minutes until crisp-tender. Remove from skillet and set aside.

Add remaining 1 tablespoon of olive oil to the skillet. Add cubed chicken, season with salt and pepper. Cook until browned and cooked through, about 6-8 minutes.

In a small bowl, mix cornstarch with 1/4 cup cold water. Stir into the skillet with the chicken. Pour prepared sauce into the skillet, bring to a boil and simmer until thickened, about 2 minutes.

Return sautéed vegetables to the skillet, toss to coat with sauce. Cook for another minute.

Garnish with chopped green onions and sesame seeds. Serve over cooked rice.