Preheat the oven to 400°F. Line a baking sheet with foil and grease it with cooking spray. (Alternately, you can grease two 13x9-inch baking dishes with cooking spray.) Set it aside.
Trim the ends off the zucchini then cut them in half lengthwise. Using a melon baller or small spoon, scoop out the centers of the zucchini, leaving a 1/2-inch border around all edges. Discard the scooped out centers or save them for another use (such as zucchini fritters). Arrange the halved zucchini on the baking sheet, cut side up, then brush them with the olive oil. Roast the zucchini for 25 minutes. While the zucchini are roasting, prepare the filling.
Add the ground turkey to a large nonstick skillet placed over medium heat. Cook the meat, breaking it apart with a spatula, until it is no longer pink. Reduce the heat to low then stir in the garlic powder, ground cumin, paprika, oregano, chili powder, 1/2 teaspoon salt, 1/4 teaspoon pepper and tomato paste.
Remove the zucchini boats from the oven then divide the ground turkey mixture evenly among them, top them with the cheese and return them to the oven just until the cheese is melted.
Remove the zucchini boats from the oven serve them with guacamole and salsa.