Steps
1. In a bowl, combine the drained tuna, ketchup, diced tomatoes, onions, cilantro, chili powder, salt, and pepper.
2. Mix well until all ingredients are evenly incorporated.
3. Place the tostada shell on a plate and spoon the tuna salad mixture on top.
4. Garnish with additional cilantro if desired.
5. Enjoy your Mexican Tuna Breakfast Tostada!