Preheat an oven to 375 degrees. Prepare 2 chicken breasts by slicing 5-7 cuts across each piece. Lay the chicken down in a glass baking dish that has been sprayed.
Finely chop the broccoli into small bits. In a bowl, combine HALF the chopped broccoli with the first amount of shredded cheddar.
Sprinkle the salt, pepper, and onion powder over the chicken breasts. Then, stuff the broccoli/cheddar mixture into the cut slices. Fill the chicken as much as you can without breaking the slices.
Bake the chicken for 45 minutes or until the cheese is golden brown and a meat thermometer reads at least 170 degrees.
While the chicken is baking, make the broccoli cheddar sauce. In a pan, combine the cream with the second half of chopped broccoli. Heat on low heat until a low simmer starts.
Add the final amount of cheddar cheese into the sauce in ¼-cup additions, whisking the cheese until it melts. When the sauce is complete, set it aside to cool and thicken slightly.
Pour the sauce over the completed broccoli cheddar hasselback chicken or set it on the side as a dipping sauce. Enjoy!