In a large pan under medium-high heat, add olive oil and chicken. Sprinkle salt and pepper over the chicken, cook for 5 minutes. Turn off the heat, remove chicken and set aside, leaving oil in the pan. Be careful not to splash yourself with hot oil.
Return the pan to medium-high heat, then add garlic, couscous and chicken stock to the pan. Cover and let simmer for about 12 minutes, until couscous is tender and chewy.
Reduce heat to low and add chicken, green beans, juice of two lemons and thyme. Stir in ricotta, season with salt and pepper, and let cook for another 5 minutes, allowing the lemon juice to soak into the couscous.
Serve with parmesan, lemon slices, lemon zest and additional thyme, if desired.