Heat olive oil in a large skillet over medium heat. Add turkey breast, green pepper, garlic, Italian seasoning, ground black pepper, salt, and red pepper flakes; cook and stir until turkey is lightly browned, 4 to 5 minutes.
Stir marinara sauce and baby spinach into the turkey mixture; cook and stir until marinara sauce is warm through, about 3 minutes.
Stir zucchini noodles into the sauce with tongs; cook and stir until the zucchini is slightly tender, 2 to 3 minutes.
