Using the Sauté function on High, heat the oil for about 1 minute, until shimmering. Add the mustard seeds, onion, cumin and salt and cook for 7 minutes, stirring occasionally, until the onions have softened and browned.
Stir in the chile and garlic; cook for about 1 minute, until fragrant. Stir in the hot water, squash and broccoli. Secure the lid and cook on high pressure for 2 minutes.
Once the cooking is complete, quick-release the pressure. Remove the lid, stir and serve.