Preheat oven to 350 degrees F.
Cook spaghetti according to package instructions using a large pot.
While spaghetti is cooking, cook ground turkey in a large skillet over medium heat with a drizzle of olive oil. Use a wooden spoon and/or spatula to break the meat up and stir it until cooked through. When meat is cooked and no longer pink, drain any grease if necessary, and transfer to a bowl. Set aside.
Rinse out the same skillet and wipe with a paper towel. Return to medium-high heat. Drizzle ~1/2 Tbsp avocado oil and add broccoli florets. Cook for about 5 minutes, until broccoli starts to brown, then add chopped onion and garlic, stirring with a spatula to incorporate. Cook veggies for an additional 5 minutes or so, or until onion is translucent.
When spaghetti is al dente, drain water using a large colander, then transfer cooked spaghetti back to the large pot. Add all ingredients to the pot with spaghetti: cooked ground turkey, broccoli, garlic and onion, marinara sauce and 1/4 cup shredded Parmesan. Stir until all ingredients are evenly incorporated.
Transfer spaghetti, turkey and veggie mixture to a greased 9x13 pan. Top with 1 cup mozzarella cheese & remaining Parmesan cheese. Sprinkle evenly over the top. Add dried Italian seasoning and fresh cracked black pepper, to taste, if desired.
Put in oven to bake for 20-30 minutes or until cheese is melted and pasta bake is hot throughout. Serve immediately.
Keep in an airtight container in the refrigerator for up to 4 days.