Cut your chicken breast into small cubes (about the size of dice). Heat 1 tbsp of oil in a large skillet or wok over medium-high heat until it's shimmering. Add the chicken and cook for 5-6 minutes, stirring occasionally, until the edges are golden and it's cooked through. Don't crowd the pan — give it space to actually sear.
Push the cooked chicken to the side of the pan. Pour the remaining 1 tbsp oil into the empty space and add your diced onion. Let it cook for 2 minutes until it starts getting soft, then add the minced garlic and stir everything together for about 30 seconds until it smells amazing.
Dump in the frozen mixed vegetables and stir-fry everything for 2-3 minutes. The veggies will start thawing and warming through. I always break up any clumps as I go — just keeps everything moving at the same speed.
Push everything to the edges of your pan, creating a well in the center. Pour the beaten eggs into that space and scramble them for 1-2 minutes until they're mostly cooked. Then mix the eggs in with all the other ingredients. Don't panic if it looks a little watery at first.
Add your 3 cups of rice to the pan, breaking up any clumps as you go. This part takes a couple of minutes but it's worth it — you want the rice separated and coated. Stir constantly so nothing sticks to the bottom, and keep the heat medium-high.
Pour in the soy sauce and sesame oil, then add the black pepper and salt. Stir everything together for about 1 minute until the seasoning is totally mixed in and the chicken fried rice recipe looks evenly coated. Taste it right now and adjust — if you want more salt or soy, go for it.
Add the sliced green onions and give it one final stir. Transfer to a serving bowl and you're done! The whole thing should take about 15 minutes from start to finish.