- Season the chicken breasts with salt, pepper, and minced garlic on both sides. 
- Turn on the Instant Pot and select the sauté function. Heat the olive oil in the pot. 
- Once the oil is hot, add the chicken breasts to the pot and sear them on both sides until golden brown, about 3-4 minutes per side. Remove the chicken from the pot and set aside. 
- In the same pot, add the mustard, honey, Splenda, and chicken broth. Stir well to combine, scraping up any browned bits from the bottom of the pot. 
- Return the chicken breasts to the pot, making sure they are coated with the sauce. 
- Close the Instant Pot lid and set the valve to the sealing position. Select the "manual" or "pressure cook" setting and set the timer for 8 minutes on high pressure. 
- Once the cooking time is complete, allow the pressure to release naturally for 5 minutes, then carefully do a quick release of any remaining pressure. 
- Open the Instant Pot lid and check the internal temperature of the chicken with a meat thermometer. It should register at least 165°F (74°C). 
- Remove the chicken from the pot and transfer it to a serving platter. 
- Stir the Greek yogurt into the sauce remaining in the pot until well combined. If you prefer a thicker sauce, mix 1 tablespoon of cornstarch with 2 tablespoons of water and add it to the sauce, stirring constantly until thickened. 
- Pour the sauce over the chicken breasts and serve hot.