In a food processor, puree ginger and garlic with 1/4 cup water until mostly smooth.
In a large saucepan, heat oil over medium-high. Add mustard seed and cumin seed and cook until fragrant, about 1 minute. Add ginger-garlic paste; reduce heat to medium-low and cook, scraping up browned bits with a wooden spoon, until most of the liquid has evaporated, 5 to 7 minutes. Add tomatoes and cook until beginning to break down, about 3 minutes.
Add potatoes and 3 1/2 cups water; season with 1 teaspoon salt and 1/4 teaspoon pepper. Increase heat to high and boil until potatoes are tender, about 12 minutes. Fold in cauliflower and okra, partially cover, and cook until tender, 9 to 10 minutes. Serve curry with rice.
To build the curry's flavor, start by cooking the spices in oil to release their aroma. Then add the ginger-garlic paste and cook until dry and thickened.