Preheat the oven to 425°F (220°C) and move the rack to the top third of the oven.

Cut the bell peppers and onion into 1/4-inch (6mm) slices.

Cut the chicken into 1/2-inch (1 cm) thick strips.

In a medium bowl, combine 2 tablespoons of oil with Fajita seasoning. Add the chicken and toss until evenly combined. Season with salt and pepper.

Heat the remaining 1 tablespoon of oil in a large frying pan over high heat. Add the chicken in an even layer. Cook it until browned then flip over and cook very briefly - do not cook the chicken completely, it should be browned but not cooked through (it will finish cooking in the oven). Transfer the chicken to a bowl and toss with lime juice.

Add bell peppers and onion to the pan. Cook for a couple of minutes until soft but still crunchy. Add the vegetables to the chicken, stir together and season with salt and pepper.

Line a large baking sheet with parchment paper. Spread the tortilla chips in a mostly even layer (it's fine if they're overlapping).

Top the nachos with 2/3 of the cheese.

Next, top it with chicken fajitas and veggies.

Sprinkle the remaining cheese on top. (If your baking sheet is a bit smaller, you can put the remaining tortilla chips, chicken fajitas and cheese in a second layer).

Place the baking sheet in the oven and bake for 10 minutes or until the cheese is melted and chicken cooked through.

Serve the nachos right away with sour cream and chopped avocado, enjoy!