Begin by cooking the rice noodles according to the instructions on the package and set aside.
Gather all the ingredients for the pad thai sauce and stir together in a small bowl.
Prepare the vegetables by mincing the garlic and onion and slicing the mushrooms. Slice the scallions and set them aside for the end to garnish.
Cut the chicken thigh into small, bite-sized pieces, removing any excess fat in the process. Weigh it to ensure you have 4 ounces (or your preferred amount) of chicken after removing the excess fat. Season with salt and pepper.
Spray a skillet with cooking spray and sauté the vegetables. Begin to add in the chicken pieces in a single layer. Cook for about 3-4 minutes on each side while stirring the vegetables around consistently to avoid overcooking and burning anything.
Once the chicken looks about done and the vegetables have softened, add in the cooked rice noodles and the pad thai stir fry sauce. Mix everything together thoroughly.
Move the mixture to one side of the side and crack in an egg on the other side. Wait for the egg to begin to solidify, then break the egg and mix it in with the noodles thoroughly.
Remove from pan, top with cilantro, chili powder, and lime, and enjoy your delicious healthy chicken pad thai!