in a small mixing bowl, mix cumin, chili powder, coriander and 1/4 tsp salt. place chicken breasts in Instant Pot and season both sides with seasoning.
cover chicken with salsa. set Instant Pot to "meat" for 13 minutes on high. Make sure vent is sealed. When done, use quick release method (press cancel, turn off and turn knob to venting). Let chicken cool. Shred with claws and return meat back to instant pot juices. Stir. (if using crock-pot - place chicken in crockpot, season, cover with salsa and set to low for 5-6 hrs)
turn on broiler and preheat a baking sheet for a couple minutes. while pan is heating, slice onions and toss with olive oil. carefully remove pan from broiler and place onions on tray. Cook for approximately 10 minutes, flipping halfway through. Keep checking on them to make sure you don't completely torch them.
in a small pot, add black beans (make sure to drain and rinse first) and 1/8 tsp salt. stirring every 30 seconds or so, heat beans for about 5 minutes or until warm to the touch.
in a medium mixing bowl, combine arugula, tomatoes, onions, beans and remaining 1/8 tsp salt. stir.
serve! top each tostada shell with approximately 1/2 cup of veggie mixture, 3oz meat, slice of avocado and a pinch of shredded cheese and cilantro. Top with cholula and lime juice if would like!