Add the garlic and tomato paste and cook for another minute, stirring frequently to prevent the garlic from scorching.
Turn the Instant Pot off, and add the lentils and water. Cover, lock the lid, close the vent, and cook on high pressure for 8 minutes. Let the Instant Pot release steam naturally for another 5 minutes. At this time, if the Instant Pot is still under pressure, carefully quick-release the valve. The lentils should be tender, but still have a slight bite.
Switch the Instant Pot back to the saute setting. Add the taco seasoning and stir. Heat until any excess liquid has evaporated and the filling has thickened (most commercial taco seasonings contain corn flour or another thickener, so the lentils should thicken within a few minutes).
Season to taste with salt.
Notes
If making these oil-free, omit the oil and saute the onion and celery together with the salt. Add a little water, if necessary, to prevent burning.
For extra veggies, add 1/2 cup sliced peppers to the onion and celery.