Set your oven to 200C/180C fan/gas 6. Use a fork to pierce the potato skins, and then place them on a baking tray. Bake for 45 minutes or until they are soft all the way through. Remove from oven and let cool. While those are cooking, heat oil in a small pan over medium-high heat Add onions and chilies cook for 8-10 minutes or until both items are soft throughout. Let that mixture cool as well.
Add the potatoes, chilli onions, sweetcorn, coriander and half the polenta to a bowl. Using your hands mix together with some spices until smooth then shape into 10 burgers; they will be quite soft. Carefully dip each burger into remaining polenta before dusting off any excess cornmeal. Place them on oiled baking trays then chilling for at least 30 mins or you can wrap and freeze them now.
Place the barbecue on low. When the flames have died down, place a large, well-oiled non-stick frying pan or a sturdy baking tray over the bars. Brown the burgers in a pan or on a tray for 10 minutes each side until golden brown. Alternatively, cook on oiled baking trays in an oven heated to 220°C/200°C fan/gas 7 for 15 minutes. Serve in buns with salsa, onion, and salad leaves as desired.