2 cans water packed tuna
1 small red onion diced
2 Plum tomatoes diced
2 avocados cut into ¼" pieces
2 cups of lettuce cut into ¼" strips Any type of loose leaf lettuce works great. Iceberg lettuce works also.
2 serrano chiles minced
2 tsp. minced cilantro
2 tsp. mayonnaise
juice from 2 Mexican limes Key limes
12 tostadas
Salt to taste