Crisp the tostadas — Heat neutral oil in a small sauté pan to 350°F. Working one at a time, fry each tostada for 10 seconds per side, until lightly golden and extra crisp. Transfer to a paper towel–lined plate to drain.
Prepare the fish — Dice the halibut into ¼-inch cubes and place in a chilled mixing bowl.
Cure the ceviche — Add lime juice and kosher salt to the fish. Gently toss to coat, being careful not to break up the cubes. Let marinate for 5 minutes, just until the fish turns slightly opaque.
Finish the mix — Fold in tomato, red onion, and cilantro. Taste and adjust salt if needed.
Assemble — Divide the ceviche evenly between the tostadas. Top with sliced avocado and a drizzle of Holbox Peanut Salsa Macha. Serve immediately while the tostadas are crisp and the fish is bright and fresh.