Preheat your oven to 375 degrees and grease a 9x13 baking dish with non-stick cooking spray.
In a large bowl, combine ricotta cheese, mozzarella cheese, Colby jack, Italian seasoning, garlic powder, and black pepper until smooth.
Add chicken and broccoli to the cheese mixture and combine well.
Spread a ¼ cup layer of alfredo sauce over the bottom of your 9x13 baking dish and cook your manicotti noodles according to the box directions, allow them to cool slightly.
Stuff your cooked manicotti noodles with the chicken broccoli mixture. The easiest way to do this is to hold the noodle in one hand and squeeze it open while using a spoon to stuff the noodle with the other hand. The noodles break easily so be careful not to stuff them too full. You can stuff them from both ends to make it easier as well.
Lay the stuffed noodles side by side lengthwise in your baking dish and cover with the remaining alfredo sauce.
Bake uncovered in your preheated oven for 25 minutes or until the sauce is bubbly and the stuffed noodles are heated throughout.
Sprinkle an even layer of shredded parmesan cheese over the noodles and place it back in the oven, uncovered, for 5 minutes or just long enough to melt the parmesan cheese.
Top with chopped parsley and serve warm.