What you need -- 1 large can of crushed tomatoes; 2 large onions, peeled and sliced as for onion rings; 500 - 600 gr of white fish fillets, (you can use almost any mild flavoured variety such as cod, pollock, haddock, basa); Sambal Oelek; salt and pepper; 2Tbs margarine for cooking.
What you do -- heat a skillet over medium high, and melt margarine. Add onion and cook until transparent and just softened enough to be able to push to the sides of the pan. Increase heat slightly, and add fish fillets. Season with salt and pepper. Brown on each side about 3 minutes. Reduce heat to medium low, and add tomatoes, and 1 - 5 Tbs of Sambal according to your taste. Simmer for 5 or 6 minutes more, then serve. Can be added as is to your buffet for Rijsttafel, or served over cooked rice or noodles.