Heat oven to 400°F. Line cookie sheet with parchment paper. Place polenta rounds on parchment-lined cookie sheet. Brush each with salad dressing. Set aside.
Melt butter in small skillet over medium-high heat. Add onion, bell peppers, brown sugar, oregano and salt. Cook about 5 minutes or until vegetables are tender, stirring occasionally. Top each polenta round with rounded 1/2 teaspoon vegetable mixture.
Bake at 400°F. for 10 to 15 minutes or until thoroughly heated. Immediately sprinkle each with Cheddar cheese. Remove from cookie sheet. Serve warm.