Roast the Jalapeno and Poblano peppers over high heat until the skin sides are fully charred. Using a sharp knife, cut them in half and remove the seeds and stems.
Add the peppers, garlic, salt, olive oil and cilantro to the blender and puree until smooth.
Add the puree to the Greek yogurt and stir until evenly combined.
The Rub and Tuna
In a mixing bowl, whisk all the ingredients together until thoroughly combined.
Cut the tuna loin in half lengthwise, then cut the halves into roughly 2-inch pieces.
Blanch each piece of tuna in boiling water for about 10 seconds, until the outside turns white. Then immediately transfer it to an ice bath. After about a minute, dab the tuna with a paper towel to remove excess moisture, then move it to the spice rub. Roll the tuna in the rub until thoroughly coated, then place it in the fridge.
Jicama Slaw
Whisk the lime juice, fish sauce and sugar together until all the sugar is dissolved. Use either a mandolin or a vegetable peeler to finely slice the jicama, then julienne it with a sharp knife.
Add the jicama to the lime mixture and store in the refrigerator for later use.
Tortillas and Assembly
Preheat the oven to 400 F.
Cut the tortillas into quarters. Place the tortillas onto a baking sheet lined with parchment paper, drizzle with olive oil, and bake until golden and crispy, about 7-10 minutes.
Remove from the oven and sprinkle with salt.
Assembly
Top each tostada shell with a dollop of the aoli, a thin slice of avocado, a slice of the spice-rubbed tuna, and a pinch of the lime-marinated jicama slaw.
Garnish with a slice of radish, a couple sprigs of cilantro, and a slice of Fresno chili. Serve with lime pieces on the side.