Preheat the oven to 450°F (230°C). Line a large rimmed baking sheet with parchment paper or lightly coat it with oil.
Place the cubed chicken on one side of the prepared sheet pan.
Sprinkle the chicken with garlic powder, black pepper, and chili flakes to taste. Toss until evenly seasoned.
Add the flour and toss again so the chicken pieces develop a thin, even coating.
Drizzle 2 tablespoons of olive oil over the chicken and toss until lightly coated. Arrange the pieces in a single layer with some space between them.
Add the broccoli florets or chopped asparagus to the other side of the pan. Drizzle with the remaining olive oil and season lightly with salt and black pepper.
Bake for approximately 10–15 minutes, or until the vegetables are tender and the chicken is nearly cooked through.
Meanwhile, prepare the sauce by combining the soy sauce or tamari, lemon juice, honey, grated garlic, gochujang, chopped green onion, and toasted sesame oil in a bowl. Stir until thoroughly combined.
Remove the baking sheet from the oven. Transfer the vegetables to a plate and keep them warm.
Pour the prepared sauce over the chicken and toss carefully until every piece is coated.
Return the 30 Minute Honey Garlic Chicken to the oven for approximately 5 minutes, or until the sauce becomes sticky and clings to the chicken.
Check that the thickest pieces of chicken have reached an internal temperature of 165°F (74°C).
Serve immediately with the roasted vegetables. Sprinkle with toasted sesame seeds and additional green onions if desired.