Place sliced chicken and flour in a zip-tight bag. Season with salt and pepper. Seal bag. Shake bag to coat chicken in flour.
Heat half the oil in a large skillet over medium-high heat. Cook chicken for 3 to 4 minutes per side, or until well browned. Transfer to a plate.
Heat remaining oil in skillet. Cook onion, stirring occasionally, for 5 minutes or until softened. Add garlic. Cook for 30 seconds or until fragrant.
Stir in chicken stock and lemon juice and let simmer for a minute.
Return the browned chicken to the skillet. Bring to a simmer. Reduce heat to low. Simmer for 5 to 6 minutes until chicken is just cooked through. Transfer chicken to a plate.
If using heavy cream, add the cream to the skillet and stir to combine.Add the cooked rice to the skillet and cook for 2 to 3 minutes or until heated through. Season with salt and pepper. Return the chicken to the skillet and cook for 1 to 2 minutes, or until the sauce is heated through.
Top with thinly sliced lemon slices and fresh parsley.