Set the Sauté function button to high and heat the olive oil for 1 minute. Add the onion, carrots, celery and garlic. Cook, stirring occasionally, until softened but not browned, about 4-5 minutes.
Add the barley, marinara sauce, chicken broth, water, chile flakes, bay leaves, salt and pepper, and parmesan rind, if using.
Secure the lid and set the Pressure Release to Sealing. Press Cancel to stop the Sauté function. Select Pressure cook or Manual setting; adjust pressure to high and set time for 18 minutes. When finished cooking, quick-release pressure and open the lid. Remove the bay leaves. Stir in cannellini beans, spinach and pesto, if using. Let warm for about 2 minutes or until spinach is wilted. Taste and add more salt and pepper, if necessary.
Serve immediately, garnished with grated Parmesan and chopped parsley and basil, if desired.
Notes
For this recipe I use a 6-quart Instant Pot.To freeze: Let the soup cool completely and then freeze individual portions in freezer bags or glass containers. Thaw in the refrigerator and warm gently in a pot adding a bit more liquid if necessary.