Preheat oven to 400°F (200°C). Line a large baking sheet with foil or parchment paper.
In a large skillet, heat 1 tbsp oil over medium-high heat. Add chicken and cook until browned and cooked through, about 5-7 minutes. Remove from skillet.
Add remaining 1 tbsp oil to skillet. Sauté bell peppers and onion until tender, about 4-5 minutes.
Return chicken to skillet. Sprinkle fajita seasoning and water over mixture. Stir and cook for 1-2 minutes until sauce thickens. Remove from heat.
Spread tortilla chips evenly on prepared baking sheet. Top with chicken and pepper mixture, then sprinkle cheese evenly over the top.
Bake for 8-10 minutes until cheese is melted and bubbly.
Remove from oven and top with dollops of sour cream, guacamole, and salsa. Garnish with cilantro and jalapeño slices if desired. Serve immediately.
Tips
For extra heat, add a dash of cayenne pepper to the fajita seasoning.
Substitute chicken with beef strips or shrimp if preferred.
Store leftover toppings separately; reheat chips in oven to crisp.