Preheat oven to 375°F (190°C). Place corn tostadas or tortillas in a single layer on a baking sheet. Brush both sides lightly with 1 tablespoon olive oil and sprinkle with 1 teaspoon sea salt. Bake 6–10 minutes, flipping once, until golden and crisp. Remove and let cool on a rack.

Tuna topping

Prepare tuna

Drain the canned tuna well and transfer to a medium mixing bowl. Use a fork to flake the tuna into small pieces.

Mix flavorings

To the flaked tuna add 3 tablespoons finely chopped sundried tomatoes, 4 tablespoons chopped pitted green olives, 2 tablespoons finely chopped red onion, and 2 tablespoons chopped cilantro or parsley. Add 2 tablespoons extra virgin olive oil and 2 tablespoons fresh lime juice. Season with 1 teaspoon smoked paprika, 1 teaspoon black pepper, and 1/2 teaspoon salt. Gently fold until combined. Taste and adjust salt, lime, or olive oil as needed.

Crunch & assembly

Toast pistachios

Heat a small dry skillet over medium heat. Add 1/2 cup shelled pistachios and toast, stirring frequently, 2–3 minutes until fragrant and lightly browned. Remove from heat and roughly chop if not already chopped.

Assemble tostadas

Divide the tuna mixture evenly among the 6 crisped tostadas, mounding it in the center of each. Sprinkle the chopped toasted pistachios over each tostada for crunch. Add a small handful (about 1–2 tablespoons) of microgreens or baby arugula on top if using.

Finish and serve

Drizzle a little extra olive oil (about 1 teaspoon divided) over the assembled tostadas and squeeze lime wedges over each to taste. Serve immediately so the tostada stays crisp.