On a 6-quart Instant Pot, select More/High Sauté. Add the oil and onion, then cook, stirring occasionally, until beginning to brown, about 5 minutes. Add the ginger and garlic; cook, stirring, until fragrant, about 30 seconds. Stir in the paprika, turmeric, garam masala and cayenne, then add 1½ cups water, scraping up any browned bits. Add the potatoes and 1½ teaspoons salt; stir to combine, then distribute in an even layer. Add the tomatoes with their juice in an even layer on top of the potatoes; do not stir.