Using a large skillet, heat oil over medium heat until very hot. Add onion and olives.
Stir occasionally, every 2-3 minutes until onion is translucent. Add tomatoes, capers, garlic, wine and red pepper flakes. Bring to a boil and simmer 5 minutes.
Meanwhile, using another skillet, melt butter over medium heat and add fish; cook 2 minutes per side until lightly brown. Remove from skillet and place in tomato mixture, cover and cook 3-4 minutes until cooked through.
Serve immediately. This works alone with a side veggie or on top of a plate of cabbage slaw or cauliflower rice for a full and satisfying meal.