Set your oven to 400⁰F/200⁰C, combination steam setting. If your oven has variable steam settings, use around 60%. If not, don't worry! Just set to combi steam at the correct temperature and the oven will figure out the humidity for you.
Scrub the sweet potatoes under running water and give each one a couple of pricks with a fork. Put them onto a baking tray and cook for about 45 minutes, or until a small knife can be pushed into the centre without any resistance.
While the potatoes are cooking, put the bacon and oil in another pan. Mix it around to distribute the oil and spread it out in a single layer. Add it to the oven for about 10 minutes, or until the bacon is crispy, then tip in the corn and black beans, give it a quick mix and put back in for another 5-6 minutes until everything is hot. If you are using frozen corn, cook it straight from frozen but maybe give it a minute or two longer.
Put the bacon/corn/beans mix into a bowl, and the spring onions and sour cream into another couple of bowls. When the potatoes are cooked, cut a slice vertically down the middle of each one, push the sides to squeeze open and create a ‘V’ for the toppings, and serve everything at the table for people to help themselves.