Add the oil to a large saute pan over medium-high heat. Add onions, garlic and the red pepper flakes. Cook until slightly caramelized for about 2 to 3 minutes. Stir in the greens and toss well to wilt. Add the sugar and broth and toss together. Turn the heat down and cover. Cook until liquid is evaporated and greens become glazed, tossing occasionally, about 6 to 8 minutes. Season with salt and pepper and transfer to a serving bowl. Serve.