In a bowl, mix cucumber with 1/2 teaspoon of salt, transfer to a colander, and leave over a bowl for 20 minutes.
Heat olive oil in a large skillet over medium-high heat. Pour the onion into the pan, cook until golden brown, about 10 minutes. Then add the garlic and cook for about 1 minute. Place the cucumber and cook for about 3 minutes. Add bell pepper, vinegar, sugar, cayenne pepper, cinnamon, and salt to taste, stir, cook for 3-5 minutes. Then add the mint, stir and transfer the contents of the skillet to a large bowl.
Melt the butter in the same skillet over medium-low heat. Sprinkle steaks with salt and place in a preheated pan, cook for about 5 minutes, then turn over and cook on the other side for another 3 minutes.
Transfer fish to plates. Put the saute back in the pan, reheat, and put on the steaks. Sprinkle with mint and serve immediately.