In a non-reactive casserole dish (such as glass or ceramic), place the fish, onion, tomatoes, salt, oregano and jalapeno. Pour lime and lemon juice over mixture. Stir all ingredients gently until combined. Let sit covered in the refrigerator for 1 hour, then stir. Let sit for 1½ hours more in the refrigerator (a total of 2½ hours), allowing flavors to blend. The fish should change from translucent to whiter in color when finished. Drain marinade and gently mix in cilantro, avocado and mango. Serve with warmed tortillas for ceviche tacos or with tortilla chips. Makes 4 to 6 servings.
Tip: Avocado will ripen on its own in 1-3 days. However, if you need to use it right away there's a faster way to soften the fruit. Prick avocado several times with a fork and place it on a microwavable plate lined with paper towels. Place the entire dish in the microwave and set the power to medium. Cook for 30 seconds, check the avocado. If it still isn't soft enough to eat, microwave for another 30 seconds. Repeat steps until the fruit is the desired softness.
Approximate Nutrient Analysis per serving (based on 4 servings):
250 calories, 10 g fat, 1.5 g saturated fat, 50 mg cholesterol, 1250 mg sodium, 18 g carbohydrate, 6 g fiber, 7 g sugar, 25 g protein
Approximate Nutrient Analysis per serving (based on 6 servings):
160 calories, 7g fat, 1 g saturated fat, 35 mg cholesterol, 850 mg sodium, 12 g carbohydrate, 4 g fiber, 5 g sugar, 17 g protein