In a large bowl, mix the butternut squash, bell pepper, Brussels sprouts, dried oregano, salt, pepper, and olive oil until the veggies are evenly coated.
Pour the vegetables onto a baking sheet in one even layer and roast for 40 minutes.
To make the dressing, place the avocado, garlic, lime juice, olive oil, salt, and pepper in a blender or food processor and blend until the mixture is light and creamy.
To assemble the salad, place a handful of mixed greens on a plate and top with the roasted veggies. Spoon on the Avocado Dressing and serve!