Begin by making the Braised Curried Chicken: In a Dutch oven over medium heat, heat the oil. Dry off the chicken thighs with paper towels and sprinkle on the kosher salt, pepper, and a teaspoon of the Spicemode Golden Curry seasoning. Add a couple of chicken thighs at a time and brown on each side. Remove the thighs to a plate after they're browned. After all the chicken is browned put it back in the pot.
As the chicken browns, in a food processor, finely chop the cilantro, tomatoes, onions, and garlic. Add this to the Dutch oven, along with the browned chicken, the other two teaspoons of the Spicemode Golden Curry seasoning and the chicken stock. Simmer, covered, on low heat, for 50 minutes.
While the chicken braises, make the Pickled Onions: Simply stir all the ingredients together in a bowl.
Also, bake the tostada shells: Preheat the oven to 400 degrees. Brush the tortillas on both sides with the oil and bake on a sheet pan for 10 minutes.
When the chicken is done, remove the chicken and shred it. Put it in a bowl and stir in some braising liquid, so that the chicken is moist but not real drippy.
To Assemble the Tostadas: Top each tortilla with some of the chicken, cilantro, queso fresco, and pickled onions.