Cut the chicken breasts into 1x1-inch cubes. Season with salt and pepper and mix it up.
Preheat the pan to medium/high heat and add olive oil.
When the oil is hot, add the chicken and brown it on all sides for about 5-7 minutes.
NOTE: At this point, we don’t need to cook the meat through, as it will finish cooking later. We just want some brown crust for additional flavor.
NOTE: If you have a lot of chicken, you can brown it in two batches. Make sure you don’t overcrowd the pan, as it will start to boil instead of browning.
When the chicken is browned, transfer it to a plate and set aside.
Add chopped onion and cook it for about 5 minutes, until it gets soft and translucent. Add minced garlic and stir for about 30 seconds to release the aroma.
Add the browned chicken back to the pot.
Now we can add rinsed rice, chicken stock, and water. Mix everything and bring it to boil. Then lower the heat to low and cover with the lid.
After 10 minutes, add chopped broccoli and stir. Cover with the lid again and cook until the rice is fully cooked, stirring occasionally.
Preheat the oven to 425°F.
When the rice is cooked, add milk and stir. Then add 1 cup of shredded sharp cheddar and fold it in.
Sprinkle the rest of the cheese on top and transfer the pan to the oven for about 10-15 minutes or until the cheese is melted and bubbling.