Line an 8×8-inch square pan with parchment paper, leaving an overhang on two sides to help lift the bars out later. Drain and rinse the soaked cashews. If using frozen berries, let them thaw slightly.

In a food processor, add the raw walnuts, Medjool dates, shredded coconut, raw cacao powder (if using), ground cinnamon, and a pinch of fine sea salt. Pulse until the mixture is crumbly but sticky; when pinched between your fingers it should hold together. If too dry, add 1 more date or a teaspoon of coconut oil; if too sticky, add a tablespoon of shredded coconut and pulse again.

Transfer the crust mixture to the prepared pan. Using clean hands or the bottom of a flat measuring cup, press it firmly into an even layer. Take your time to compact it well so the bars hold together. Place the pan in the refrigerator while you prepare the filling.

In a high-speed blender, combine the soaked cashews, coconut milk, maple syrup or agave, lemon juice, vanilla extract, melted coconut oil, and a pinch of fine sea salt. Blend on high until completely smooth, 1–3 minutes, stopping to scrape down the sides as needed. You are aiming for a silky, pourable mixture with no graininess. If it is too thick to blend smoothly, add 1–2 tablespoons more coconut milk and blend again.

Remove the crust from the fridge. Pour the cashew filling over the crust and spread it into an even layer with a spatula. Gently tap the pan on the counter a few times to release any air bubbles.

In a small blender cup or food processor, combine the mixed berries, maple syrup, chia seeds, and lemon juice. Blend until mostly smooth. Taste and add a little more maple syrup if you prefer a sweeter swirl. Let the mixture sit for 5–10 minutes so the chia seeds can thicken it slightly.

Spoon small dollops of the berry mixture over the surface of the cashew layer. Using a thin knife or skewer, gently drag through the dollops to create swirls and patterns. Make only a few passes (about 3–5) so you keep a nice contrast between the cheesecake layer and the berry swirl.

Cover the pan and chill in the refrigerator for at least 4 hours, or in the freezer for 1½–2 hours, until firm enough to slice. The refrigerator gives a softer cheesecake texture, while the freezer gives a more ice cream bar-like texture.

Use the parchment overhang to lift the set slab out of the pan and onto a cutting board. With a sharp knife warmed under hot water and wiped dry, cut into 12–16 bars or squares. Serve chilled, topped with extra fresh berries, shredded coconut, or a drizzle of raw vegan chocolate if desired.