
Step 1 · Make the Dressing
In a medium bowl, mix together the garlic, serrano, lime juice, mayonnaise, ½ teaspoon salt and ½ teaspoon pepper until well combined; set aside.
Step 2 · Make the Salad
Roughly chop the cilantro, chop the avocado, dice the red onion and tomato, and place everything in the bowl with the dressing. Add the tuna and ¼ teaspoon salt and toss until combined. Taste and add more salt as desired. Serve immediately, or cover and refrigerate for up to two days.
Step 3 · Assemble the Tostadas
When you are ready to eat, divide the filling among the tostada shells (about a generous ½ cup tuna salad for each tostada) and top with hot sauce, if desired.