Heat the oil over very low heat. Add the onion, cook and stir until onions become translucent. Stir in mushrooms and sun-dried tomatoes. Simmer covered until the mushrooms are tender.
Season with salt and pepper to taste.
Remove from the heat and add the basil.
To make the sauce
Heat olive oil over very low heat. Add garlic and cook and stir until it releases its aroma, do not let it burn. Stir in the tomatoes and simmer covered until they are very soft.
Remove the twigs from the oregano and add the leaves to the pan. Season with salt and pepper to taste.
Using a potato masher, mash the sauce over the heat until there are no big clumps.
Pour into a sauce dish.
To make the base
Preheat oven to 350ºF [175 .
Cover a 2 quart-baking pan with olive oil.
Mix polenta, water, sweet corn, raisins, salt and sugar in a deep pot. Cook over medium heat stirring constantly. When the polenta is cooked and it starts lifting from the bottom remove from the heat.
Grease a 9"[23 cm] square baking pan.
Pour half of the polenta mix and spread in an even layer. Top with the filling and smooth it out. Spread the remaining polenta mix in an even layer and smooth it out with a fork.
Place in the oven and cook until the top is light golden.
Serve with fresh, green salad, olives and warm bread.
If you don't have peeled tomatoes, just make a superficial cross cut at the bottom of the tomatoes and dunk in abundant boiling water. Remove from the water when the peel starts to come off and finish peeling.If the polenta is sticking to your spatula or fork just cover them in olive oil, the polenta will slide right off.