Preheat oven to 400 F. Once cauliflower is divided into florets, add to a large bowl and mix with melted butter, garlic powder and barbecue sauce. Stir to distribute mixture evenly over cauliflower florets.
Cover baking sheet with aluminum foil and spread cauliflower florets evenly across baking sheet. Cook for 20-25 minutes, turning halfway.
Fill tortillas with roasted cauliflower, avocado cilantro sauce, sliced red cabbage and tomatoes. Serve warm.
Avocado Cilantro Sauce
Add avocado, cilantro, sour cream, spices and lime juice to a blender or food processor. Pulse until mixture is homogenous and smooth.