Cut okras vertically into halves, then slice into 2cm pieces. Set aside.
Heat oil in a pan over medium-high heat. Saute onion, stirring occasionally, for 3 minutes, or until light brown. Add ginger and green chilies. Saute, stirring, for a minute, or until aromatic. Add okras. Cook, stirring, for 5 minutes or until tender crisp. Add tomatoes. Saute, stirring, for a minute.
Reduce heat to low. Add ground turmeric, ground coriander, chilly powder, and enough salt. Saute, stirring, for a minute, or until aromatic. Increase the heat to medium-high. Add thin coconut milk. Bring to the boil. Reduce heat to low. Simmer for 3 minutes. Add thick coconut milk. Sprinkle garam masala on top, and season with ground black pepper. Remove from flame.