Indian Spiced Cauliflower and Potatoes

Name: Indian Spiced Cauliflower and Potatoes
Ingredients: 1 (1 3/4-lb) head cauliflower, cut into 3/4-inch-wide florets; 1 1/4 lb Yukon Gold potatoes, peeled and cut into 1/2-inch cubes; 5 tablespoons vegetable oil; 1/2 teaspoon cumin seeds; 3/4 teaspoon salt; 1 medium onion, finely chopped; 2 garlic cloves, finely chopped; 2 teaspoons minced fresh jalapeño, including seeds; 2 teaspoons minced peeled fresh ginger; 1 teaspoon ground cumin; 1/2 teaspoon ground coriander; 1/4 teaspoon turmeric; 1/4 teaspoon cayenne; 1/2 cup water; Accompaniment: lemon wedges