Mix tuna, mayonnaise, and salsa together in a bowl. Set aside.
Heat vegetable oil over medium-high heat in a frying pan. Add tortillas in batches and fry until golden and slightly crisp, 2 to 3 minutes.
Spread tuna mixture over tortillas evenly. Top with tomato, spinach, and onions. Sprinkle with Cheddar cheese and top with avocado slices.
