In a medium-sized bowl, toss together sliced strawberries, lemon juice and zest, maple syrup and vanilla and set aside.
Preheat oven to 350ºF (177ºC) and prepare parchment-lined 8x8-inch baking dish.
In a large mixing bowl, combine oats, flour and brown sugar. Add butter and work it in well with a fork until the mixture is crumbly with the butter evenly distributed.
Spread 2/3 of the oat mixture into the bottom of the baking dish, pressing it down to form a base. Bake for 15 minutes.
Remove pan from oven. Spoon strawberry mixture over the base, spreading it out to the edges of the pan. Then sprinkle remaining oat mixture across the top.
Bake for 20-25 minutes until lightly browned. Remove from oven and let cool on a wire cooling rack for at least 30 minutes. Slice into squares with a sharp knife and serve.