Turn on your Instant Pot and select the Saute mode on high.
Add olive oil, roasted red diced tomatoes and onions. Saute until onions are soft, about 3 minutes.
Add garlic. Continue to saute for an additional 2 minutes.
Toss shrimp in cajun seasoning until coated evenly. Place shrimp into Instant Pot and saute for 2-3 minutes on each side until shrimp are slightly pink in color.
Once shrimp are slightly pink in color, remove from Instant Pot with tongs and place aside in a large bowl.
Add heavy cream, cream cheese, Parmesan cheese and stir so all ingredients in the Pot are mixed together well. Saute until thickened, about 10 minutes. NOTE: do not clean out the pot. You will want all the Cajun goodness to cook into the sauce.
Once the sauce has reached your desired thickness, add to large bowl with shrimp and set aside.
Select the 'cancel' function to reset the Instant Pot cooking function. Select 'Pressure Cook' on high.
Add pasta shells and chicken broth. Stir until mixed well. Pressure cook on high for 3 minutes. NOTE: we like our pasta very slighly al dente. If you like yours more soft, you may want to cook for 4 minutes.
Once the timer beeps, quick release all pressure. Carefully remove the lid.
Add shrimp and sauce to the pasta and mix until all ingredients are well combined.
Serve hot and enjoy!