Preheat oven to 400 F degrees. Spray a baking sheet with cooking spray.
Wash the potatoes and cut the end off. Slice the potatoes into slice that are about 1/4 inch (7mm) in thickness. Season potatoes with salt and pepper. Bake for 20 minutes, turn the slices over and bake for another 30 minutes.
In the meantime, heat the olive oil in a skillet over medium heat. Add onions and cook until it's slightly translucent. Add the peppers and the fajita mix and toss. Cook until peppers onion is golden brown and peppers are cooked.
To assemble top each potato slice with a tsp or so of sour cream, followed by the onion and pepper mixture, salsa, and green onions. Season with salt and pepper.
These bites, because of all the sauce, can get a little weird kept as leftovers for too long. I wouldn't keep them longer than a day or two. You won't be able to reheat them once they're assembled, but I promise they'll still taste good cold.
If you think you might be left with extra, you can assemble a few at a time as they're needed. The leftover potatoes and onion/pepper mixture will last about 3-5 days in the fridge.
Please keep in mind that nutritional information is a rough estimate and can vary greatly based on products used.