Add the beans, arugula, olive oil, garlic, red pepper, zest, and juice of half the lemon to a blender. Season generously with salt and pepper. Pulse a few times to combine. The texture should be creamy and rustic. Taste the dip and adjust with more lemon juice or salt and pepper if needed.

Transfer the dip to a small bowl and drizzle with extra olive oil and red pepper flakes. Arrange your sourdough slices on the side, to serve for dipping.