Warming sweet potato and bean chili

Name: Warming sweet potato and bean chili
Prep time: 30 min
Total time: 30 min
Cuisine: American, Mexican, Latin American
Ingredients: 1 sweet potato; 7 oz kidney beans (canned); 7 oz black beans (canned); 5.33 oz quinoa; 1 bell pepper; 1 onion; 2 cloves garlic; 3.5 oz corn (canned); 1.8 oz walnuts; 1 tsp chili powder; 0.5 tsp paprika powder; 0.5 tsp cayenne pepper; 1 tsp ground cumin; 1 tbsp dried oregano; 28 oz crushed tomatoes; 1 cup vegetable stock; 1 tbsp soy sauce; 2 tbsp cane sugar; 1 avocado; 5.33 oz soy yogurt; oil for frying; lime juice to taste; cilantro for serving; salt; pepper