For the crust, in a medium saucepan set over medium heat, combine the water, masa harina and salt. Cook, whisking constantly, until very thick, about 5-6 minutes. It should be the consistency of very soft sugar cookie dough.
Carefully press the dough into an oiled 8 or 9-inch cast iron skillet or a similar-sized pie plate. Lightly grease or water your hands if needed so the dough doesn't stick while pressing. Bake the crust until firm, about 30 minutes.
While the crust is baking, in a large nonstick skillet, heat the oil and add the garlic powder, cumin, oregano and coriander. Cook until fragrant, about 30 seconds. Add the refried beans and cook until heated through, about 1 minute. Spread this mixture over the cooked crust.
Wipe out the skillet with a paper towel and set it over medium heat. Saute the ground beef (or turkey) with the chopped onion and 1 teaspoon salt and 1/2 teaspoon pepper, until the meat is cooked through, about 5-6 minutes.
Drain the grease from the skillet. Add the cumin and chili powder and stir to combine. Spread this mixture over the refried beans and transfer the skillet/pie plate again to warm through, 5-10 minutes.
Meanwhile, puree the avocado, cream cheese, cilantro, lime juice and garlic in a food processor blender until smooth. Season with salt and pepper to taste.
Remove the pie from the oven. Spread the avocado mixture over the top of the ground beef and garnish the pie with shredded cheese, lettuce, corn chips, sour cream or any other taco toppings you like. Serve the pie warm or at room temperature (if serving at room temperature, don't top with the avocado mixture or toppings until ready to serve).
Notes
Masa Harina: is a corn flour used to make tortillas and tamales. It is widely available in the Mexican foods-aisle of most grocery stores.