For the Chili Cream Sauce:

• 1 cup nonfat sour cream
• 1 tablespoon fresh lime juice
• 2 teaspoons chili powder
• 1/2 teaspoon ground cumin
• Salt and freshly ground black pepper

To Finish the Sushi:

• 4 8-inch flour tortillas
• 1 ripe avocado
• 1 tomato, peeled and seeded
• 1 bunch cilantro, separated into sprigs
• 8 pickled jalapeno chilies, thinly sliced lengthwise (optional)
• 8 scallions, green part only

Directions:

Brush the tuna with the oil on both sides, sprinkle with the chili powder and season with salt and pepper. Heat a nonstick frying pan over high heat. Sear the tuna on both sides (1 to 2 minutes per side for rare, 2 to 3 minutes per side for medium). Transfer the tuna to a plate and let cool. (Alternatively, the tuna can be grilled or broiled.)

Roast and peel the poblano and yellow pepper. Cut them into long, 1/4 inch strips. Blanch the spinach in boiling salted water until tender, about 30 seconds. Drain, chill in ice water, drain again and blot dry with paper towels.

Make the chili cream sauce: Put the sour cream, lime juice, chili powder and cumin in a nonreactive mixing bowl and whisk to combine. Season with salt and pepper: the sauce should be highly seasoned. Place half the cream sauce in a small serving bowl to serve as a dipping sauce.

Preheat the oven to 350 F. Place the tortillas on a baking sheet and heat until soft and pliable, 2 to 3 minutes. Meanwhile, peel and pit the avocado and cut it into long, 1/4 inch strips. Cut the tomato into long, 1/4-inch strips. Slice the tuna into long, 1/4-inch strips.

To assemble the "sushi," lay a tortilla on a work surface. Spread 1 tablespoon of the remaining cream sauce evenly over the surface. Arrange a thin layer of spinach on top of this. Starting at the edge closest to you, arrange strips of tuna, avocado, tomato, roasted peppers, cilantro, jalapeno and scallion in neat horizontal rows, leaving the last inch of tortilla uncovered. Roll up the tortilla tightly and wrap in plastic wrap. Repeat with the remaining tortillas. Let the "sushi" stand 10 minutes before cutting.

Just before serving, using a very sharp, slender knife, cut each "sushi" roll crosswise into 1-inch sections. (Do not serve end sections that look ragged.) Stand the sections on end and arrange them on a platter around the bowl of dipping sauce.

Note:

You can substitute 16 large, peeled and deveined shrimp for the tuna. Impale them end-to-end on a bamboo skewer to keep them straight during cooking. Poach in simmering water until just firm, about 1 minute. Season with salt and pepper, omitting the chili powder.