For the tortillas: Heat the oil in a heavy, high-sided pan to 350 degrees F. Fry the tortilla pieces a few at a time until lightly golden brown and crisp. Drain on a plate lined with paper towels and season with salt.

For the avocado butter: Combine all ingredients in a blender and blend until smooth.

For the tartare: Combine tuna, mustard oil, olive oil, capers, chipotle, cilantro, and green onion in a large bowl. Gently fold in the avocado and season with salt and pepper, to taste.

Place each of the fried tortilla pieces on a plate and spread with a small dollop of the avocado butter. Top the butter with some of the tuna tartare. Repeat with the remaining ingredients.