if okras are not your thing replace them with green beans. Malaysian fish curry powder can be bought from Asian supermarkets. (note: i didn't strictly follow every step. adjust measurements to your own taste :)
process garlic and onion to a smooth paste in a spice blender, adding a little oil if needed to keep the mixture turning,set aside.
mix curry powder with 4 tbsp water to form a paste,set aside.
soak tamarind pulp in 500ml (2 cups) of water for 5 minutes, then squeeze and strain to obtain juiceset aside.
heat oil in a wide saucepan,add mustard seeds, fenugreek, cumin and curry leaves. fry until mustard seeds start to pop (around 30 seconds)add the garlic onion paste, stir fry over low heat until mixture smells fragrant and starts to brown (about 5 minutes).
add curry paste and cook over low heat until dry and oil starts to separate (8 to 10 minutes).add tamarind juice and bring to a boil.
add fish and okras, tomatoes, chillies, coconut milk, salt. simmer gently about 10 minutes (or until fish and okras are cooked through).