Turn on the Instant Pot to the sauté setting and add the oil.
Sauté the sausage with the onion, bell pepper, garlic, salt, pepper, Italian seasoning and red pepper flakes for about 3 minutes.
Added the Rotel and stir until combined.
Pierce the spaghetti squash and place on top of the sausage mixture.
Turn the Instant Pot to the Pressure Cooker setting. Set at high pressure for 15 minutes.
Let the pressure naturally release for 10 minutes.
Remove the squash when it's cool enough to handle. Cut lengthwise with a large knife.
Scoop out the seeds leaving the strands in place.
Transfer each half to a large plate and, using a slotted spoon, top evenly with the sausage mixture.
Sprinkle shredded cheese over the top (to taste) and enjoy immediately.