Prepare all your ingredients before you begin cooking, as the recipe moves quickly once started. Cut the vegetables into bite-sized pieces—make sure the broccoli is cut into small florets so everything cooks evenly. In a medium bowl, combine all the sauce ingredients and whisk them together thoroughly. Slice the chicken into 1-inch pieces and place them in a bowl. Sprinkle with garlic powder and pepper, then mix well. Add the cornstarch and stir until each piece of chicken is evenly coated. Heat 2 tablespoons of olive oil in a deep skillet over medium-high heat, allowing the pan to warm up for a few minutes.

Cook the chicken in two batches for the best browning. Shake off any excess cornstarch before adding half of the chicken to the skillet. Cook for about 4 minutes, then flip and cook another 3 to 4 minutes until browned and cooked through—using tongs makes flipping easier. Transfer the cooked chicken to a plate, then repeat with the remaining chicken, adding the last tablespoon of olive oil to the skillet. If the pan looks dry, add a small splash (about a teaspoon) of olive oil, then add the onions and cook for 1 minute, stirring occasionally.

Next, add the broccoli and red bell peppers to the skillet and cook for about 3 minutes, stirring frequently, until the vegetables are tender-crisp. Cook longer if you prefer softer veggies. Return the chicken to the pan and pour in the sauce (give it a quick whisk again before adding). Stir constantly as the sauce bubbles and thickens, which should take less than a minute, ensuring everything is evenly coated. Remove from heat and serve immediately.