Select the sauté setting on a 6-quart Instant Pot or electric pressure cooker. Add the butter. When the butter melts, add the mushrooms, onion, and sweet pepper. Cook, stirring, until the vegetables are tender, about 6-8 minutes. Season with 1/2 teaspoon of salt and 1/2 teaspoon of pepper. Add the garlic and cook an additional minute.

Stir in the flour and cook for another minute. Gradually whisk in the chicken broth. Bring the mixture to a boil, stirring constantly, until it thickens slightly, about 1-2 minutes. Stir in the cream and the noodles.

Place the top on the Instant Pot and lock the lid. Make sure the vent is closed.  Select manual, adjust the pressure to high and set the time to 3 minutes.

When the time is finished, do a quick-release to release any remaining pressure.

Combine the tuna, lemon juice and the remaining 1/2 teaspoon salt and 1/2 teaspoon pepper in a small bowl.

Select the sauté setting on the Instant Pot and stir in the tuna mixture, the cheese, and the peas. Cook for a few minutes, just until heated through.

Serve the tuna casserole topped with the crushed potato chips.