If using a multi-function pressure cooker or slow cooker or a Dutch oven you will be able to do this in one pot. If not you will need a large skillet.
Remove casing from sausage and brown over medium heat, crumbling evenly. About 5 minutes. Add onion, garlic, sweet red pepper and sun-dried tomatoes. Cook another 5 minutes. See Note 1 for Variations.
Sprinkle oregano, salt and pepper over mixture and cook 1-2 minutes, stirring. See Note 2 for Variations.
If you were sauteeing in a skillet, transfer the mixture to your pressure cooker or slow cooker.
Stove Top- Add the broth and crushed red pepper, if using, to the mixture you sauteed in your Dutch oven. Simmer for 20 minutes. Add the spinach and evaporated milk and return to a simmer. Simmer another 5 minutes or so until spinach is wilted.
Pressure Cooker- Add the broth and crushed red pepper, if using, to the sauteed mixture. Set pressure to high and cook 5 minutes. Use quick release; return cooker to sautee mode; add the spinach and the milk and cook until spinach is wilted and soup is heated through. This make take 3-5 minutes further.
Slow Cooker- Add the broth and crushed red pepper, if using, to the sauteed mixture. Cook on high 4 hours or low 7-8 hours. Add the spinach and evaporated milk during the last hour of cooking.
All Methods- Serve immediately with grated parmesan for garnish and additional hot sauce if desired.
Soup stores well in the fridge for 2-3 days. It may be even better the second day once flavours have permeated even more. Soup can be frozen for months and reheated as desired.