Melt 1 Tbsp. butter in a medium saucepan over medium-high heat. Stir in orzo and cook about 3 minutes, stirring frequently, until toasted. Stir in 3 cups of stock, salt and pepper; bring just to a boil. Reduce heat to medium-low and simmer 5 minutes, stirring occasionally. Stir in broccoli and cook about 3 minutes until orzo is tender.  Cover, remove from heat and set aside. 

Heat oil in a large skillet over medium heat. Meanwhile, place flour in a shallow dish. Season chicken with salt and pepper, then dip in flour on both sides to coat, shaking off any excess. Add chicken to the skillet and cook 5 to 6 minutes per side, until golden brown and cooked through (165°F internal temperature). Transfer to a serving dish and cover loosely with foil to keep warm.

Add 1 Tbsp. butter and garlic to the skillet and cook 30 seconds on medium-high heat. Add lemon juice and remaining chicken stock, scraping up any browned bits in the pan; reduce heat and simmer 8 to 10 minutes until sauce is reduced by half and starts to thicken slightly.

Remove skillet from heat; whisk in remaining 4 Tbsp. butter until melted. Season to taste with salt and pepper. Stir lemon zest into orzo. To serve, spoon orzo and broccoli onto plates or in shallow bowls.  Top with chicken; spoon sauce over chicken and garnish with parsley and lemon slice, if desired.