Preheat oven to 350°F. Grease or line a 9×13-inch baking dish with parchment paper.
In a large bowl, whisk together the Pioneer mix, sugar, eggs, milk, melted butter, vanilla, and lemon zest (if using) until smooth.
Gently fold in the chopped strawberries.
Pour the batter into the prepared dish and smooth the top.
Bake for 30–35 minutes, or until golden brown and a toothpick inserted in the center comes out clean.
Let cool slightly. Slice into squares or bars.
Top with fresh whipped cream, sliced strawberries, and a dusting of powdered sugar. Serve warm or chilled.