For the Quick Pickled Onions: Place sliced onions in a large bowl and cover with hot water for 5 minutes.

Meanwhile, in a jar or bowl large enough for all the onions, whisk together the apple cider vinegar, kosher salt, peppercorns, and coriander seeds until all the salt has dissolved.

After soaking, drain the water from the onions and add them to the bowl with the brine. Cover and refrigerate for at least 30 minutes.

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

Add the spices to the melted ghee and gently toast, stirring occasionally until fragrant, about 2 minutes.

Add the tomato paste to the skillet and stir for about 1 minute until well combined.

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. Taste and add more salt and pepper if desired.

Heat a skillet over medium heat, adding 1 tsp of oil per tortilla.

Add each tortilla to the skillet and cook, flipping every 2 minutes, until crisp, about 5 to 6 minutes total. Place crispy tortillas on a wire rack and set aside.

To assemble, spread guacamole on the bottom of each tostada. Top with romaine, shredded chicken, cilantro, and quick pickled onions. Serve with a wedge of lime.