Toss sliced bell peppers and onions with one tablespoon olive oil; season with salt and pepper. Then, spread out on a foil lined baking sheet and broil for 15 minutes.
In a large frying pan, sauté chicken in remaining olive oil until there's no pink color left.
Add chicken, peppers, onions, crushed tomatoes, fajita seasoning, and water to large sauce pan and let simmer for 10 minutes.
Plate spaghetti, top with sauce, and enjoy!
Don't be afraid to experiment by taking other fajita toppings like sour cream, cheese or shredded lettuce and adding them on top of your spaghetti.