Preheat oven to 400°F and lightly coat a 9x13-inch baking dish with nonstick spray.
Slice zucchini in half lengthwise and scoop out centers, reserving the flesh into a bowl. Arrange zucchini in baking dish, cut side up.
4 medium zucchini
Heat oil in a saute pan over medium-high. Cook chicken until cooked through and lightly browned, 3-5 minutes. Add onion and reserved zucchini and continue to cook for 1 minute.
1 tablespoon olive oil, 1 pound boneless chicken breasts or thighs, 1/2 cup diced onion
Mix together chili powder, cumin, oregano, paprika, and salt, and sprinkle over chicken. Stir to coat and cook for 2 minutes. Stir in salsa, lower heat to medium-low, and let simmer for 5-10 minutes, until thickened.
1 teaspoon chili powder, 1 teaspoon cumin, 1 teaspoon Mexican oregano, 1/2 teaspoon paprika, 1/2 teaspoon fine sea salt, 1/2 cup prepared salsa
Divide chicken mixture into zucchini (you might have extra filling) and top with cheese.
Shredded pepper jack cheese
Cover with foil and bake for 35 minutes, until zucchini is tender.