Spray a deep nonstick pan with nonstick cooking spray and heat over medium heat. Add onion and sauté for 10 minutes, stirring often.
Add in the garlic and cook another 3 minutes, stirring often.
Add in the olives, vinegar, and pepper, cook for 10 minutes; stir often.
While cooking add the lemon juice, sugar, and chili powder into a medium bowl, stir well; add in the fish pieces and 1/2 cup of cooked onion mixture, gently stir to coat.
Preheat oven to 375 degrees F.
Add the water to the remaining onion mixture in the pan, bring to a boil over high heat. Remove from heat, fold in the tortilla chips about 4-5 times over the next 2-3 minutes, allowing the chips to become soft and absorb most of the liquid.
Place tortilla mixture evenly into the bottom of a 10 x 12 inch baking dish.
Remove fish and onion from bowl with a slotted spoon and place on top of tortilla mixture. Throw out the marinade.
Place in oven and bake until fish flakes easily when tested with a fork, about 10 minutes. Serve immediately.