Cooking fish in parchment paper couldn't be easier but be careful when opening each packet as the steam inside is very hot. Slideshow: Healthy Fish Recipes
Preheat the oven to 400º. Fold each square of parchment in half and cut with scissors into a heart shape. Unfold and top one half of the heart shape with a piece of tilapia, sprig of rosemary, sliced garlic and tomatoes. Drizzle each with one tablespoon of the olive oil, squeeze with a lemon quarter and season with salt and pepper. Fold the parchment over and beginning at the pointed end of heart-shape, fold and crimp edges around to tightly seal. Repeat with all four packets and place on two baking sheets.
Bake in the oven for 20 minutes. Remove from the oven and place on individual plates. Tear open the top of the parchment and serve.
The packets can be made up to two hours ahead and refrigerated. Bake for 25 minutes if coming straight from the refrigerator.