Preheat oven to 425F.

Look for fish fillets that are of fairly even thickness, no more than 1 inch thick. If using chicken breasts, trim to 6 ounces and pound to an even thickness between two sheets of plastic. Spritz with a little lemon juice and season evenly on both sides with salt and pepper or Creole seasoning; set aside while you prep the remaining ingredients.

For each serving, toss baby spinach (or mixed baby greens) and halved grape tomatoes with salt, pepper, 1/2 teaspoon lemon juice, 1 teaspoon each minced garlic and shallot, a pinch of the fresh minced herbs, and a drizzle of olive oil. Mound the spinach in the center of a sheet of parchment paper or foil large enough to generously encase the fillet or breast. Top with a few thin slices of onion.

Top with the fish or chicken, spritz with a little more lemon juice, tuck a few lemon slices in, and gather the parchment paper up around the packet; carefully pour in a tablespoon of cream or broth, and seal the edges tightly with several folds. Transfer to a rimmed baking sheet and bake for about 12 minutes. Carefully test a packet for doneness after about 10 minutes. Serve with hot cooked rice.