Place sliced onions in a large bowl and cover in hot water for 5 minutes. Meanwhile, whisk together the apple cider vinegar, kosher salt, peppercorns, and coriander seeds in a jar or bowl until the salt has dissolved.

Drain the water from the onions and add them to the brine. Cover and refrigerate for at least 30 minutes before serving.

Heat a skillet over medium heat and melt the ghee or butter.

Add the spices and gently toast, stirring occasionally for about 2 minutes.

Add the tomato paste and cook while stirring for about 1 minute.

Add the chopped green chiles and chicken broth, bringing the mixture to a gentle simmer.

Add the shredded chicken and toss until well coated in the sauce. Adjust salt and pepper to taste.

Heat a skillet over medium heat and add 1 tsp of oil per tortilla.

Cook each tortilla, flipping every 2 minutes, until crisp all over, about 5 to 6 minutes total.

Place each crispy tortilla on a wire rack and set aside.

Spread guacamole on each tostada, top with romaine, shredded chicken, cilantro, and quick pickled onions.

Serve with a wedge of lime.