Cook the ground beef mixture by heating 1 tablespoon of oil in a large skillet over medium-high heat. Add the onion and cook, stirring often, for 4-5 minutes.
Add the ground beef, breaking it into crumbles with a spatula as it browns, and cook, stirring often, for 4-5 minutes.
Add the garlic and cook, stirring constantly, for 1 minute. Drain excess grease, then add the taco seasoning. Toss to coat evenly and cook for 2 minutes.
Add the water and simmer for 10 minutes. Taste and add salt and pepper if needed.
Prepare the crispy tostada shells by preheating the oven to 225 degrees and lining a baking sheet with parchment paper.
Cook the crispy tostada shell by filling a small skillet with vegetable oil ½ inch up the sides. Heat the oil over medium-high heat until very hot, about 7-10 minutes. Test the oil by dipping the tip of a corn tortilla into the hot oil; if it bubbles a lot, it’s ready. Side Note: Your tostada will be soggy if you add the tortilla to oil that is not hot enough.
When the oil is HOT, carefully place 1 corn tortilla in the hot oil, then poke a few holes in the center with a fork to let steam exit.
Fry one tortilla at a time, holding the metal potato masher upright on the tortilla to keep it submerged until crisp and lightly browned, about 45 to 60 seconds. Flip and cook for 45-60 seconds, or until golden brown.
Drain both sides on paper towels, then immediately sprinkle with a bit of sea salt and set aside while you repeat the process with the other tortillas.
To serve the tostadas, spoon a little refried beans, followed by the ground beef mixture. Top with shredded lettuce, tomatoes, avocado slices, green onions, cotija cheese, and crema.
Serve immediately with salsa and hot sauce on the side. Enjoy.