In a large skillet, heat the olive oil over medium heat. Add the chopped onion and minced garlic, sautéing until the onion is translucent, about 3-4 minutes.
Add the ground turkey to the skillet. Cook, breaking it apart with a spatula, until browned and cooked through, about 5-7 minutes.
Stir in the diced red bell pepper and zucchini. Cook for another 5 minutes, or until the vegetables are tender.
Add the diced tomatoes, Italian seasoning, salt, and black pepper. Stir to combine and let simmer for an additional 5 minutes.
If using, sprinkle the shredded mozzarella cheese on top and cover the skillet for 2-3 minutes until the cheese is melted.
Remove from heat and garnish with fresh basil if desired. Serve warm.