Preheat the oven to 350 degrees F.
Heat 2 tablespoons of the olive oil in a large nonstick skillet over medium-high heat. Add the turkey and cook, while stirring and breaking up the meat with the back of a wooden spoon, until browned, about 3 minutes. Stir in the peppers, zucchini and onions, and saute until the veggies have started to soften, about 5 minutes more. Sprinkle the meat with the chili powder, cumin and paprika and give a good seasoning of salt and pepper; cook until fragrant. Stir in the chopped tomatoes and cook until the tomatoes have broken down and are soft, about 2 minutes more. Add the chicken broth and simmer lightly until the sauce is thickened and all the vegetables are tender, about 15 minutes.
Add 1 to 2 tablespoons olive oil to a small bowl and season with a pinch of salt. Lightly brush both sides of the tortilla shells with the olive oil. Carefully place each tortilla shell over two bars of the oven rack. Bake until crisp, 8 to 10 minutes. Remove the shells with tongs after they are baked.
Serve the warm taco shells filled with the turkey veggie filling and topped with lettuce, cheese, avocado, tomatoes, radishes and sour cream.