Turn Instant Pot to sauté (High). Heat olive oil.
Add onion and garlic. Sauté 1 minute.
Add zucchini, carrots, and celery. Sauté another minute.
Add pasta sauce (or diluted tomato paste) and stir well.
Press Cancel.
Add beans, broth, Italian seasoning, and pasta shells. Mix.
Lock the lid and pressure cook 5 minutes on High.
Quick release.
Add salt, pepper, and spinach. Stir to wilt.
Serve hot with cheese and garlic bread.