For the tostada shells

1. Prep oven. Heat oven to 450 degrees F.
2. Prep tortillas. Spray both sides of each tortilla with cooking spray. Lay tortillas on a baking sheet.
3. Bake. Bake tortillas in oven for 8 minutes flipping the tortillas halfway through. When tortillas are crisp, remove baking sheet from the oven and turn the oven to broil.

For the guacamole

1. Mix. In a medium bowl, stir together onion, jalapeño, tomato, garlic, and cilantro.
2. Add avocado. Cut the avocado in half lengthwise around the pit. Twist the avocado halves in opposite directions and pull the halves apart. Scoop out the avocado pulp with a spoon and add to the onion mixture.
3. Season. Add lime juice and salt.
4. Mash. With a spoon or fork, roughly mash the avocado while mixing in the onion mixture until evenly combined. Taste and season with additional lime juice or salt as needed. Set aside.

For the chicken

1. Cook onions. Heat olive oil in a heavy skillet over medium-low heat. Add onions and cook, stirring occasionally, until onions are lightly browned, about 10 minutes. Don’t be tempted to rush this step, the caramelized onions add a lot of flavor.
2. Add chicken & spices. Add shredded chicken, cumin, paprika, and salt. Sauté until mixture is heated through and chicken is evenly coated with spices.

For serving

1. Assemble tostadas. Spread guacamole on each tostada shell and then top with chicken mixture, dividing the guacamole and chicken mixture evenly among the tostada shells. Sprinkle cheese on top.
2. Melt cheese. Place the baking sheet under the broiler just until the cheese melts, about 2 minutes. Remove pan from oven, sprinkle tostadas with chopped cilantro leaves and serve.