Juice and zest one lemon, measuring out 2 tablespoons of juice and 1 tablespoon of zest. Add all ingredients to a food processor including 1/2 cup oat flour, 1/2 cup vanilla protein powder, 1/3 cup cashew butter, 1/4 cup maple syrup, 2 tablespoons ground flax seed, 1 tablespoon coconut oil, 1 teaspoon vanilla extract, and 1/4 teaspoon salt. Pulse until well blended and the dough forms a ball. Check the texture by rolling a small amount of dough into a ball. It should hold together without sticking to your fingers. Add a spoonful of yogurt if dry, or a light sprinkle of oat flour if sticky. Line a standard bread pan with parchment paper, leaving some overhang for easy removal. Transfer the mixture to the pan and press firmly to create an even layer. Place in the freezer for about 10 minutes to firm up before adding the topping.
In a microwave-safe bowl, combine 2 tablespoons white chocolate chips with 1 teaspoon coconut oil. Microwave in 25-second increments, stirring between each, until completely melted and smooth.
Lift the bars out using the parchment paper overhang and cut into 6 bars. Drizzle over the chilled bars. Store in the refrigerator until ready to enjoy.