Preheat the oven to 350F and grease a 9-x-13 inch pan.
Whisk the ricotta, sugar, eggs, melted butter, vanilla, lemon zest and juice together. In a separate bowl, sift the flour, baking powder, baking soda and salt. Add this to the ricotta mixture and stir just until blended. Spread this in the prepared pan.
For the streusel, stir the flour, sugar, baking powder and cinnamon together and then stir in the butter until the mixture is evenly combined. Sprinkle the raspberries over the ricotta cake (if using thawed frozen berries, drain excess juices and toss the berries with 2 Tbsp of flour) and top the fruit with the streusel. Bake the cake for 45 to 55 minutes, until a tester inserted in the centre of the cake comes out clean. Cool the cake in the pan, before serving.
The cake will keep, wrapped and unrefrigerated, for 3 days.