Preheat the oven to 375°F (190°C).
Heat 1 tablespoon of olive oil in a large skillet over medium heat.
Add the chopped onion and garlic to the skillet and sauté for 3-4 minutes until softened.
Add the ground beef to the skillet and cook, breaking it apart with a spoon, until browned and cooked through, about 6-8 minutes.
Stir in the diced zucchini, carrot, and mushrooms. Cook for another 5 minutes until the vegetables are tender.
Add the crushed tomatoes, dried oregano, dried basil, smoked paprika, sea salt, and black pepper to the skillet. Stir well to combine and simmer for 5 minutes to let the flavors meld.
Remove the skillet from heat and stir in the chopped fresh parsley.
Drizzle the remaining 1 tablespoon of olive oil over the hollowed bell peppers.
Stuff each bell pepper generously with the beef and vegetable mixture.
Place the stuffed peppers upright in a baking dish.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
Remove the foil and bake for an additional 10 minutes to lightly brown the tops.
Remove from the oven and let cool for 5 minutes before serving.