Fry the onions in some oil until soft, then add the corn (remove it from the cobs with a sharp knife). Fry for about another 3-4 minutes. Then leave it to cool for a few minutes.
Mix the beaten eggs, polenta, milk, baking powder and flour in a large bowl until smooth. Then add the two thirds of the cheese.
Mix in the onions and sweetcorn.
Grease an 8 inch silicone pan and pour in the polenta, onion and sweetcorn mixture.
Halve the tomatoes and chop the other vegetables, and place them on top, pressing in slightly.
Place the pan in your slow cooker. Put some water under your pan if your slow cooker cannot be used dry.
Cook on high for two hours approx or until a skewer or knife comes out clean.
Drizzle on a little olive oil, sprinkle on some mixed herbs, then sprinkle on the rest of the cheese on top and brown in a hot oven for 10 minutes.Serve warm.