Preparation:

In a shallow dish or zip top bag, combine the marinade ingredients.  Add the tuna; coat well, and allow to marinate for 15 minutes at room temperature.

Heat a heavy skillet, preferably cast iron, over high heat.  When hot; drain the tuna and add to the skillet with any marinade that clings to the fish (discard remaining marinade).  Immediately add the tomato, red onion, poblano and green onion tops.  Fry 1 - 2 minutes, stirring constantly. Avoid overcooking.  Fish should be seared on the outside, and just pink on the inside.  Stir in the olive oil, salt, pepper and cumin.  Divide mixture into 4 warmed flour tortillas; top with sour cream and cheddar cheese.  Serve at once.
Per Serving: 649 Calories (35.2% from fat); 25g Fat (7g Sat, 13g Mono, 3g Poly); 55g Protein; 48g Carbohydrate; 4g Dietary Fiber; 84mg Cholesterol; 1378mg Sodium.  Food Exchanges: 2 1/2 Grain (Starch); 6 1/2 Lean Meat; 1 1/2 Vegetable; 4 Fat.