Preheat your oven to 400°F. Line a large rimmed baking sheet with parchment paper and set it aside.
In a large bowl, toss together the butternut squash, carrots, fennel and red apple with the olive oil, salt and black pepper until evenly coated, then spread out onto your prepared baking sheet in a single layer. Transfer the baking sheet to your oven and roast, stirring once halfway through the cooking time, for 40 minutes. The fruits and vegetables should be soft and starting to brown in places. Remove the baking sheet from your oven and set it aside for about 10 minutes to cool slightly.
Once cool enough to safely handle, transfer all of the roasted fruits and vegetables to your blender. Add in about 2 cups of the vegetable broth. Blend on high until smooth. Then pour the contents of your blender into a large heavy-bottom pot and stir in 2 more cups of the vegetable broth. Place the pot over medium heat and bring the soup to a simmer. Stir in the cheese tortellini and cook them in the soup according to the package instructions, generally about 7-9 minutes. If the soup is getting thick, you can add in the remaining cup of vegetable broth. Taste and add more salt and pepper, if desired.
To serve, ladle the warm soup into bowls. Garnish with some of the reserved fennel fronds and a sprinkling of red pepper flakes, if desired.
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