Turkey Meatball Sandwich

Name: Turkey Meatball Sandwich
Ingredients: ½ of an onion, chopped; ½ of a green bell pepper, chopped; 3-4 garlic cloves, chopped; 28-ounce (794g) can crushed tomatoes, including the juices; 2 tbsp (5g) chopped fresh parsley; 2 tsp (8g) sugar, to taste; 2 tsp (1g) crushed oregano; 1 tsp (0,5g) basil; 1 tsp (0,5g) crushed red pepper, optional; Dash of black pepper; Dash of salt, to taste; 1 6-ounce (170g) can tomato paste; ¼ cup (10ml) water, optional, depending on the desired consistency; 1 pound (454g) ground turkey {or chicken}; 1 tbsp (2,5g) chopped parsley; 3 tbsp (7,5g) finely chopped spinach; ¾ tsp (1,8g) garlic powder; 1 tsp (5g) salt; ¼ tsp (0,6g) black pepper; 1 tsp (2g) paprika; ½ tsp (1,2g) crushed red pepper; ½ tsp (1,2g) cayenne pepper; ¾ tsp (2,5g) fennel seeds; ¼ cup (30g) feta cheese crumbles; 4 hoagie rolls; 4-8 slices of provolone cheese; ½ cup (85g) sliced pepperoncini peppers; Parmesan cheese, to taste