In a large skillet on medium heat, warm avocado oil and add ground beef and onion. Brown beef until thoroughly cooked (approximately 10 minutes) and stir in taco seasoning until well combined.
In a 9x13 glass pan, add one third of the marinara sauce. Evenly distribute half of the corn tortillas, one third of the marinara sauce, and one half of the cheese, ground beef, tomatoes and cilantro. Repeat this step.
Cover the glass pan with foil and bake for 30 minutes. Take off the foil and bake for another 10 minutes.
In a medium bowl, add avocado, sour cream, milk, cilantro, garlic powder and salt and pepper to taste. Whisk until smooth to form the avocado crema drizzle.
Once the casserole has cooled, add the avocado and drizzle the avocado crema drizzle.