1. 1. Preheat the oven to 400°F (200°C).

2. 2. Peel and dice the sweet potatoes, red onion, and chili pepper.

3. 3. Place the diced sweet potatoes, red onion, and chili pepper on a baking sheet. Drizzle with olive oil, salt, and pepper. Roast in the oven for 20-25 minutes, or until tender and slightly crispy.

4. 4. Meanwhile, season the fish fillets with salt, pepper, and fresh lemon juice.

5. 5. In a skillet over medium heat, cook the fish fillets until they are flaky and cooked through, about 3-4 minutes per side.

6. 6. Assemble the tacos by placing a spoonful of the roasted sweet potato mixture on a tortilla, topping with a cooked fish fillet, and garnishing with fresh cilantro leaves.

7. 7. Serve hot and enjoy!