Combine rice, tomatoes, feta, olives, and basil. Season mixture to taste with salt and pepper.
Slice tops off peppers, then remove seeds and membranes.
Fill peppers with rice mixture. Set aside.
Prepare Tomato Sauce:
Press Saute button on Instant Pot.
Add olive oil and garlic to pot. Mix constantly as pot heats and cook just until garlic is fragrant. Do not burn.
Turn off Instant Pot (press Cancel), then carefully stir in tomato sauce, water, basil, oregano, and crushed red pepper. Season sauce to taste with salt and pepper.
Cook Peppers:
Place a rack in the Instant Pot (over sauce), then place peppers on rack.
Secure lid and set pressure release valve to sealing. Select Pressure Cook (or Manual) button, then set to High Pressure for 8 minutes.
When time is up, do a Quick Release, then open lid.
Top each pepper with 1 tablespoon mozzarella, then replace lid and let peppers sit for 1 minute.
Carefully remove peppers from Instant Pot and transfer to plates. Season sauce with additional salt and pepper, if desired.
Serve peppers with tomato sauce, sprinkled with basil. Enjoy!
Notes
*To make rice in Instant Pot: rinse 1 ¼ cups long grain white rice in a fine mesh strainer until water runs clear. Drain well. Combine rice and 1 ¼ cups water, plus ½ teaspoon salt, in Instant Pot. Secure lid and set pressure release valve to sealing. Select Pressure Cook (or Manual) button, then set to High Pressure for 3 minutes. When time is up, let pressure release naturally for 10 minutes. After 10 minutes, do a quick release to let out any remaining pressure. Open Instant Pot and remove inner pot. Fluff rice with a fork, then let cool completely before using.