Add water to the bottom of your Ninja Foodi or Instant Pot. Put the steamer rack in the water and place whole chicken breasts on the rack. Season chicken breasts with salt, pepper, 1 tbsp of Italian seasoning, and garlic powder.
Set the Ninja Foodi or Instant Pot to the pressure cooking setting on high for 15 minutes. Quick release when finished. Remove to a bowl or cutting board to shred and set aside.
While chicken cooks, preheat your oven to 375°F. Spray 13x9 inch casserole dish with nonstick spray.
While chicken cooks, place rice and one can of chicken broth in a small pot. Bring to a boil then reduce heat to low, covering and cooking for 15 minutes.
While chicken and rice are cooking, make the sauce. Melt the whole stick of butter over medium high heat, stirring frequently to prevent burning. It will help to cut the butter into smaller pats rather than trying to melt the whole stick at once.
Once butter is melted, add onion and garlic, cooking until softened. Once softened, add flour and whisk together well to make a roux. Season with salt and pepper and let the roux cook until it is golden brown.
Once roux is golden brown, slowly whisk in remaining can of chicken broth and milk until thick and bubbly. Add mayonnaise, curry powder, lemon juice, Italian seasoning and salt and pepper to taste. Whisk well until smooth.
Add the hot cooked rice on top of the uncooked broccoli, then add the shredded chicken on top of the rice. Top the rice, chicken and broccoli mixture with the sauce. Sprinkle cheese on top.
Bake uncovered for 20 minutes or until cheese has formed a crust on top of the sauce. If a crust hasn't formed, broil for a couple minutes or until cheese is browned.