Prep the Veggies: Begin by peeling and roughly chopping the sweet potatoes and butternut squash into similar-sized pieces (about 1 inch). Place them directly into your slow cooker.
Sauté Aromatics: In a skillet, warm the sesame oil over medium-high heat. Add the diced onion and cook for 2-3 minutes until it becomes soft and fragrant. Stir in the minced garlic and chopped ginger, cooking for an additional 1-2 minutes until they soften. Carefully transfer this aromatic mixture to the slow cooker with your prepped vegetables.
Slow Cook: Pour in the low-sodium vegetable broth. Add half of the miso paste, the red pepper flakes, and a pinch of kosher salt. Give everything a good stir to combine. Cover your slow cooker and cook on LOW heat for 4 to 5 hours, or on HIGH heat for 3 to 4 hours, until the vegetables are tender.
Add Tofu & Miso: Towards the end of the cooking time, drain the block of soft or silken tofu and cut it into cubes. Remove the lid from the slow cooker and gently stir in the tofu and the remaining miso paste.
Blend to Creamy Perfection: Using an immersion blender, blend the soup directly in the slow cooker until it reaches a smooth and creamy consistency. Alternatively, carefully transfer the soup in batches to a regular blender and process until pureed. If you prefer a thinner soup, add a splash more vegetable broth until desired consistency is achieved.
Serve & Enjoy: Ladle this wholesome, creamy soup into bowls. Garnish generously with a drizzle of chili oil, fresh sliced green onions, and a sprinkle of toasted sesame seeds. Serve immediately and savor every comforting spoonful!