In large saucepan, heat oil over medium-high heat. Add onions and cook, stirring often, until softened, 4 to 5 minutes. Stir in flour and cook, stirring, 1 minute.
Slowly stir in coconut milk, broth and curry. Cook mixture until thick and bubbly, 2 to 3 minutes.
Add carrots, bell pepper, sweet potato, cauliflower and broccoli. Reduce heat to medium-low, cover and cook, until vegetables are tender, about 10 minutes. Stir in mint and cook 5 minutes more. Serve hot over basmati rice if desired.