Pat the fish dry and season with salt and pepper. Dust with flour and shake off the excess. Sauté the fillets in olive oil for one minute on each side. Be careful not to burn the roux that is being created in the bottom of your skillet, as you will be using this next. Lay the fillets in a single layer, overlapping slightly, and set aside in a baking dish.
Add the butter to the pan and melt; sauté the garlic, being careful not to burn the butter and garlic. Add the wine and the chicken broth, and bring to a low boil. Once boiling, stir in the lemon juice, zest from 1 lemon, cannellini beans, and red pepper flakes.
Top the fish with the cannellini bean mixture and bake for 10 -12 minutes.
While fish and beans are baking, sauté spinach in the same pan until wilted. (I sauté a little garlic in butter and add a pinch of red pepper flakes before sautéing the spinach.)
In a separate pot, bring the chicken broth to a a boil. Add salt to taste, zest from 1 lemon, red pepper flakes, and couscous. Cover with a lid, turn the heat off, and let sit till ready to serve. When ready to serve, fluff with fork. If needed, add more hot chicken broth.
Plate the fish and bean mixture on top of the couscous and spinach and serve with lemon slices.