Saute the onion in a hot saute pan sprayed with vegetable spray, over medium heat until the onion is golden, approximately 5 minutes.
In a large bowl mix the next 12 ingredients together. Season, to taste.
Place each tostada in the middle of each salad plate and scoop 4 ounces into the center of each tostada. Garnish with a sprig of cilantro and a wedge of lime.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.