3 tablespoons vegetable oil
1/2 teaspoon black mustard seeds
2 1/2 teaspoons cumin seeds
1 clove garlic, minced
1 medium cooked waxy potato, cut into 1/4 inch dice
1 medium tomato, cut into 1/4 inch dice
4 tablespoons chopped cilantro
3 tablespoons chopped mint leaves
1-2 fresh hot green chiles, or more to taste
2 cups fresh corn kernels
3 ounces coconut milk
3/4 teaspoon salt
1 tablespoon lemon juice
cayenne pepper, to taste