In a small bowl, whisk together the vinegar, brown sugar, and chili flakes until the sugar has dissolved. Set aside.
Heat the olive oil in a large skillet over medium heat. Add the garlic and lemon peel and cook briefly until beginning to turn golden brown, about 1 1/2 to 2 minutes. Add the vinegar mixture and salt and simmer 2 minutes longer.
Pour dressing over half the broccoli florets and serve immediately.
Hot Lemon Garlic Oil:
Heat the olive oil, garlic, and lemon peel over medium heat and let sizzle gently for a few minutes until garlic is lightly browned. Add lemon juice, salt, and pepper and heat for another minute. Pour dressing over half the broccoli florets and serve immediately.