Chop the onions, and peel and roughly chop the carrots. (Don't chop the carrots finely...2-inch chunks are best.)
Add the olive oil to the bottom of the Instant Pot, then add the veggies, and push the "Saute" button.
Cook the veggies, stirring as needed, for about five minutes, until they begin to soften.
Rinse and drain the split peas, then add them to the Instant Pot along with 5 cups of water.
Lock the lid, cancel "Saute," and push the "Manual" button. Set the timer for 15 minutes under pressure.
When the timer beeps, let the pressure come down naturally for 10-15 minutes, then if you like you can release the rest of the pressure manually.
Open the pot carefully, and add the salt and lemon juice. Stir to combine, and serve stopped with optional cubes of ham.