On a 6-quart Instant Pot, select Normal/Medium Sauté. Add 1 tablespoon of the oil and heat until shimmering. Add the couscous and cook, stirring often, until golden brown, 6 to 9 minutes. Using a large spoon, transfer the couscous to a small bowl; set aside. Add the remaining 2 tablespoons oil, the onion, garlic, cumin and 1 teaspoon salt, then cook, stirring occasionally, until they begin to brown, 6 to 9 minutes. Add 2 cups water and scrape up any browned bits. Stir in the couscous, squash, 1½ teaspoons salt and ½ teaspoon pepper, then distribute in an even layer.