Preheat the oven to 350 degrees (only if you plan to use cheese.)
Heat 1 tbsp olive oil in an oven-safe 12-inch skillet over medium-high heat. Once hot, add in the diced onions, and diced bell peppers. Sauté for 2-3 minutes. Add in minced garlic and stir for 30 seconds. Stir in the tomato paste and stir to coat the veggies.
Move veggies to the outside of the pan and add the ground beef. Let cook without stirring, until golden brown on bottom, about 1-2 minutes add the salt and seasonings and then break up into chunks. Continue to cook and crumble the ground beef until browned, incorporating veggies as you cook through the ground beef, about 5 more minutes.
Add the grated zucchini and marinara sauce. Stir to incorporate and stir to heat through.
Optional: Sprinkle with cheddar cheese and immediately transfer the skillet to the oven. Bake for 4-5 minutes or until cheese is melted.