In a large pan over medium-high heat, heat the oil and saute the onion and bell pepper for 3 minutes. Add garlic, butternut squash, and cumin and saute for 5 minutes, or until all the veggies are tender and the butternut squash is cooked all the way through.
Add half of the butternut squash and veggie mixture to each tortilla. Add a dollop of beans and avocado sliced to each tortilla, and add any other burrito fixings. Roll tightly into a burrito.