Combine the crushed tomatoes with the garlic and herbs. Cut the sausage into bite-sized chunks and mix it with the tomato mixture.
Put half the peppers and onions (unthawed) into the bottom of your slow cooker. Dump the sausage mixture on top, then the rest of the peppers and onions. Add salt and pepper and cook on low for 6 hours. Serve atop your pasta substitute of choice.
Freeze the sausage/tomato/garlic/herb mixture. You can also add the frozen veggies but there's no need since they're already bagged and frozen. When ready to cook, just dump everything into the crock pot, no need to thaw first. You may need to add an hour or two to the total cook time. You can also freeze cooked spaghetti squash flesh in muffin cups.