For the polenta:Coat a 8 in glass baking dish with cooking spray. In a large saucepan combine 2 cups water with broth, mustard and cayenne, bring to boiling. Reduce heat to medium and whisk in cornmeal. Reduce heat to medium low, cover and cook 5 minutes or until thickened, stirring occasionally. Remove from heat, pour into baking dish, set aside to get firm.
For the ragout: Preheat oven to 425 degrees. Cut off and discard dark green top from the leek, cut it into 1 inch slices and put in a large bow. Add cauliflower, carrots, mushrooms and garlic, drizzle with oil and toss to coat. Spread vegetable in a large roasting pan. Roast for 8 minutes.
Remove pan from oven and stir in corn and tomatoes. Put back in the oven for 20-25 minutes or until the vegetables are tender. Remove from oven and put vegeetables and juices in a large dutch oven.
Put dutch oven over medium heat. Cook vegetables for 5-10 minutes or until thickened. Stir in basil, majoram and thyme.
Meanwhile preheat broiler with top rack 4-6 inches from heat source. Line a baking sheet with foil and coat with cooking spray. Cut polenta into 12 squares and place on baking sheet. Broil 5-8 minutes or until lightly browned.
To serve; place 2 polenta squares on each plate and top with ragout.