Fish with Squash and Indian Seed Pop

Name: Fish with Squash and Indian Seed Pop
Ingredients: 2 medium cucumbers—peeled, seeded and finely diced; 2 medium summer squash—halved, seeded and finely diced; Kosher salt and freshly ground pepper; 6 scallions, white and tender green parts only, thinly sliced; 1 large jalapeño, seeded and minced; 2 tablespoons minced cilantro; 2 tablespoons minced mint; 2 tablespoons fresh lime juice; 1 teaspoon finely grated lime zest; 1 cup plain yogurt; 1/2 teaspoon minced garlic; 2 tablespoons extra-virgin olive oil, plus more for grilling; 1 teaspoon cumin seeds; 1 teaspoon mustard seeds; 1 teaspoon black onion seeds (nigella), optional; Four 6-ounce skinless grouper or sea bass fillets