Add the diced tomatoes, lentils, white beans, chopped celery, chopped carrots, chili powder, salt, pepper, basil, oregano and paprika to your slow cooker.
Add the vegetable broth and stir all the ingredients together. Turn on the slow cooker and cook the chili on high heat for 2-3 hours or on low for 4-5 hours, stirring every hour or so.
About 1 hour before the chili is done, preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius). Slice the sweet potatoes in half lengthwise and arrange them insides-up on a baking sheet.
Drizzle the olive oil over the sweet potato halves and sprinkle the tops with a pinch or two of salt and pepper. Bake the sweet potatoes for about 40-50 minutes, or until they can be pierced easily with a fork.
When the sweet potatoes are cooked through, slice them down the centre about half way to make room for the chili. Top each one with as much of the White Bean and Lentil Chili as each sweet potato half will hold.
Add a dollop of Greek yogurt or sour cream on top of each one, along with some shredded cheese of your choice and some chopped green onions for colour and freshness.
Serve while hot, and enjoy!