In a plastic baggie, lightly pound your chicken breasts one by one a few times until they are an even thickness (or purchase the smaller chicken tender pieces, which are already uniform). Season both sides with salt and pepper and set aside.
Combine 2 cups chicken broth, ¼ cup lemon juice, garlic and red pepper flakes in a liquid measuring cup and set aside.
Chop & measure out your onions and zucchini (if using), butter, parsley <g class="gr_ gr_168 gr-alert gr_gramm gr_inline_cards gr_disable_anim_appear Punctuation only-ins replaceWithoutSep" id="168" data-gr-id="168">and</g> lemon slices so they are ready to go.
Place a medium pot on the stove filled with chicken broth and oil/butter for your couscous.
In a large sauté pan, heat your oil over medium-high heat. Once you see the oil begin to shimmer slightly, add in your chicken and brown on each side for approximately 3-4 minutes (depending on thickness). Flip once. Remove chicken to a plate and cover with foil.
Add in your chicken broth, lemon, garlic & red pepper mixture. Scrape up any brown bits and allow mixture to simmer until reduced by half.
Meanwhile heat your chicken broth for your couscous. Once that comes to a boil, remove from heat, add in couscous, cover and allow it to stand for 4 minutes. Fluff with a fork and set aside covered until needed for assembly.
Once the chicken broth mixture in your saute pan has reduced by half, add in zucchini, remove from heat, whisk in butter until fully dissolved. Whisk in heavy cream. Season with a little salt and pepper and if you like additional red pepper.
Add chicken back into the pan and heat for 1-2 minutes over low, just to rewarm the chicken. Do not heat over high as you don't want to “break” the added cream with too much heat.
Scoop couscous onto a platter or casserole dish, place chicken over top (whole or sliced) and spoon sauce over top. Garnish with lemon slices and enjoy.