Spaghetti Napolitan (Japanese Ketchup Pasta)

Name: Spaghetti Napolitan (Japanese Ketchup Pasta)
Prep time: 15 min
Cook time: 15 min
Total time: 30 min
Cuisine: Japanese
Ingredients: 8 cups water; 1/2 tablespoon salt; 7 ounces spaghetti; 2 teaspoons vegetable oil; 1 green bell pepper , thinly sliced; 1/2 small onion, thinly sliced; 1/4 pound sausage or ham, sliced; Kosher salt, to taste; Freshly ground black pepper, to taste; 1/3 cup ketchup; 2 teaspoons butter; C hopped parsley , for garnish; Hot sauce, such as Tabasco or Tapatio, for serving