Begin by preparing your marinara sauce. Heat the olive oil in a saucepan over medium heat. Add the onion and the bell pepper and cook for 4-5 minutes until tender.
Add the garlic and cook for another minute. Add the tomato sauce, paste, water, herbs de Provence, salt, pepper and sugar.
Stir to combine and bring the sauce to a boil.Reduce the heat to medium-low and simmer for 10-15 minutes.
Remove from heat and set aside until you are ready to use. You may transfer the sauce to a blender if you would like for the sauce to be smooth.
Be careful as the the sauce is hot. This step is completely optional depending on your personal preference.
Preheat your oven to 375 F and grease a 9×13 inch baking dish. For the meatballs: In a large bowl, combine the ground beef, Italian sausage, egg, breadcrumbs, garlic powder, salt, pepper, oregano, thyme and Parmesan cheese.
Mix the ingredients together so that they are combined thoroughly. Spread a layer of marinara on the bottom of your prepared baking dish.
Form the meat into 1 1/2 inch diameter balls and place them into the baking dish (you should have about 15-16 total). Once you have formed all of your meatballs, cover them with the rest of the marinara.
Place in the oven and bake for 35-40 minutes, or until the meatballs are completely cooked through (use a meat thermometer to bring them to your desired temperature, roughly 160 F—remember that you are dealing with pork here). Remove from oven, put dish on a rack and let them stand for 2-3 minutes.
Serve the meatballs by placing three in a split hoagie roll and topping with mozzarella cheese. You may stick them under the broiler at this point, if you wish to melt the cheese. Otherwise, serve immediately and enjoy!