Preheat oven to 400˚F. Lightly spray tortillas with cooking spray. Bake until crisp and light golden.
Lightly spray a nonstick skillet with cooking spray and heat over medium-high heat. Cook fish 8-10 minutes until opaque. Flake into bite-size pieces.
Dress tortillas with lettuce topped with warm fish and dot with pesto, top with diced tomatoes.
For the Mexican Pesto: In a food processor, combine the chilies, cilantro, arugula, oregano or marjoram, garlic, cumin, lime zest and juice, pistachios or pepitas, and season with salt and pepper. Pulse-chop to combine, adding a splash of water to loosen. Turn the processor on and add the EVOO in a slow stream, blending until a thick sauce forms. (Makes 1 1/2 cups)