Turn on the Instant Pot and heat the oil on the Sauté function. Add the onion, carrots, and celery, and sauté 4 to 5 minutes until they start to soften.
Add the potato, garlic, thyme, black pepper, bay leaf, and liquid smoke. Sauté 1 minute.
Add the split peas and broth and stir to combine.
Cancel the Sauté function, place the lid on the Instant Pot and lock it in place. Set the steam release valve to Sealing.
Use the Manual function to choose 12 minutes on High Pressure.
When the 12 minute cook time is up, the Instant Pot will beep several times. Let the pot release some pressure naturally for 10 minutes. Then, carefully switch the steam release valve to Venting to release the remaining pressure. The Instant Pot will be on the Keep Warm function now. You can turn it off at this time or leave it on if you want to keep it warm for a longer time.
Carefully open the lid. Take out the bay leaf.
Stir in the diced tomatoes, if using, squeeze of lemon, and salt, as needed.
Taste and adjust seasoning as necessary, adding more thyme or liquid smoke.
Serve hot with Smoky Tempeh Crumbles (directions follow).