Bring a large pot of water (about 2 liters) to a boil and add 1 tablespoon of the salt. Add the spaghetti and cook until slightly softer than al dente. Drain and set aside.
While the pasta cooks, heat the olive oil in a large skillet or pot over medium heat.
Add the cubed salami and cook, stirring, until browned.
Reduce heat to medium-low and add the diced onion, bell pepper, olives, crushed garlic, and capers (if using). Cook, stirring, about 1 minute or until the onion becomes translucent.
Stir in the diced tomatoes and oregano, cover, and simmer 3–5 minutes until the tomatoes are softened.
Add the tomato sauce and vinegar (omit vinegar if using evaporated milk). Stir to combine and heat through.
If using evaporated milk, stir it in now and mix gently; do not let the sauce boil once milk is added to prevent curdling.
Add the drained spaghetti to the sauce and toss until evenly coated. Season with the remaining salt and black pepper to taste.
Serve hot and garnish with grated Parmesan cheese if desired.
