Prep sweet potatoes: Preheat oven to 425°F (220°C). Brush or drizzle olive oil over all sides of the sweet potatoes. Place them face-down on a baking sheet and sprinkle the top side with salt.
Roast sweet potatoes: Bake for 20 minutes. Check for doneness with a spatula, preserving the caramelized surface. Bake for an additional 10–15 minutes if needed to cook through and caramelize the underside.
Cook chicken: Heat 1 tbsp olive oil in a large skillet over medium-high heat. Add onion and sauté until soft and fragrant. Add ground chicken and taco seasoning; brown thoroughly while breaking it up with a spatula.
Finish chicken: Stir in salsa and salt. Cook for 1–2 minutes, then cover to keep warm until ready to serve.
Make chipotle sauce: Whisk together Greek yogurt, mayonnaise, chipotle powder, garlic, salt, and 2–3 tbsp water until smooth. Adjust seasoning to taste.
Assemble stacks: Layer sweet potato, chipotle sauce, spicy chicken, and toppings in that order. Optionally, drizzle more sauce on top before serving.