Select Sauté and adjust to High heat. Add the olive oil to the pot and heat until it shimmers. Add the onion and garlic. Cook, stir-ring, for 2 to 3 minutes, or until the vegetables start to soften. Add the sun-dried tomatoes and cook for 1 minute, or until fragrant.
Pour in the crushed tomatoes and stir to combine, scraping the bottom of the pot to loosen any vegetables that might be stuck. Stir in the oregano, red pepper flakes, and salt.
Lock the lid in place. Select Pressure Cook or Manual, and adjust the pressure to High and the time to 12 minutes. After cooking, release the pressure naturally for 10 minutes, then quick release any remaining pressure. Unlock the lid.
Let the sauce cool for about 10 minutes, then taste and adjust the seasoning, adding more salt if necessary. Refrigerate for up to a week or freeze for 4 to 6 weeks.