Start by prepping all your fresh fruits since they'll oxidize quickly once cut. Hull and quarter the strawberries into 1-inch pieces, then slice the bananas into 1/2-inch rounds. Leave the grapes whole—they're perfect as-is. Arrange all prepped fruits in a large mixing bowl. I like to prep the fruits just before final assembly to keep them as fresh and firm as possible, especially the bananas which brown quickly.
Pour the peach pie filling over the fresh fruits in the bowl. Drizzle the fresh lemon juice evenly over everything. The acidity from the lemon juice will help preserve the color of the bananas and strawberries while brightening all the flavors. Gently fold everything together using a spatula or large spoon, being careful not to crush the berries.
Just before serving, scatter the fresh mint chiffonade over the top of the fruit salad and gently fold it through with one or two passes of the spatula. I prefer to add the mint at the very last moment so it stays vibrant and aromatic rather than wilting into the fruit. Serve immediately for the best texture and flavor.