Cut the spaghetti squash in half diagonally. Scoop out the seeds and place both halves in the instant pot on the steamer rack. Add 1 cup of water to the pot, put the top on, make sure the valve is closed, hit "manual" and reduce time to 7 minutes.
While the squash is cooking, cook the bacon and mushrooms. Cut the bacon into small pieces and cook in a medium to large skillet over medium heat. Once crispy, remove and place on a plate. Leave about 1 tablespoon bacon grease to pan and add in the mushrooms. Cook over medium heat until tender.
Once the squash is done, hit "cancel" and release the valve. When the pin drops, open the lid and carefully remove squash to a bowl to cool a little. Once cooled enough to handle, shred into a large bowl (possibly the one you're already using) and squeeze out all the water.
Add the bacon, mushrooms, green onion, salt and half the tomatoes to the spaghetti squash and mix well.
Preheat the oven to 350° Line a 13x9 with parchment paper and add in the spaghetti mixture.
Break the eggs into a medium bowl or measuring cup and whisk until well mixed and all yolks are broken. Pour over spaghetti mixture and mix a little to make sure it's combined and spread evenly.
Top with the other half of tomatoes and bake for 50 minutes or until eggs are set.