Instructions
Step 1
Rinse the onions with boiling water and drain.
Step 2
In a large, 1 L Mason jar, mix the salt, sugar, vinegar, water and hot pepper flakes. Add the rinsed onions and marinate at room temperature for at least 30 minutes.
Step 3
Mix the tuna and lime juice in a bowl, using a fork. Salt and pepper to taste, and adjust seasoning as desired.
Step 4
Distribute the tuna mixture evenly on the 4 tostadas. Garnish with cherry tomatoes, avocado, marinated onions and fresh cilantro. Add pepper and serve with lime quarters and hot sauce.