Heat your pressure cooker with a splash of oil and when hot, add the onion, celery, and bell pepper, cook until softened, stirring often.
Add the tomatoes and mix well, then add the salt, pepper, and curry powder and mix together.
Add the water and lentils, mix and scrape the bottom of the pot to loosen any cooked on bits.
Now add the lid and lock into place, add the weight (jiggler), turn heat up to high and when the jiggler starts venting pressure and turning (hence the name jiggler, as it jiggles while doing this), start your timer for 10 minutes and reduce the heat to low or medium to maintain the venting of pressure.
When 10 minutes have passed, turn off the heat and move the cooker to an unused burn and allow the pressure to vent naturally.
When the cooker gives you indication that zero pressure inside the vessel, remove the weight, then open and remove the lid.
This can be served as a side dish or as main, and as I understand it, a common way is served on top of polenta.