Heat oven to 450°. Coat a large rimmed baking sheet with nonstick cooking spray.
Place cauliflower on prepared baking sheet and season with 1/4 tsp of the salt and the black pepper. Lightly spritz with cooking spray. Bake at 450° for 20 minutes, turning once. Remove from oven and reserve.
Heat a large nonstick pot over medium-high heat. Coat with nonstick cooking spray; add chicken and cook 6 minutes, turning once. Remove to a plate.
Add onion and red pepper to pot and cook 5 minutes. Stir in curry, ginger, sugar, cinnamon, cayenne, remaining 1 tsp salt, the broth and tomato sauce. Bring to a simmer and add reserved chicken. Simmer 10 minutes. Stir in cauliflower and heat through. Serve over cooked couscous.