If the dates are not very soft, cover them with hot water for 5 minutes, then drain and pat dry.
Place the oats in the bowl of the food processor and pulverize them until you have a fine oat flour. Alternatively, you can use store-bought oat flour. See note below.
Add the pitted dates, tahini, maple syrup, vanilla, and salt to the oat flour. Blend until the mixture forms into a sticky dough (it should turn into a ball). If it feels dry, add a spoon of plant-based milk a teaspoon at a time until the dough just sticks together when pressed.
Transfer the dough to a large bowl. Fold in 1/2 cup of the chocolate chips into the dough using a silicone spatula.Note: If the dough is too sticky to handle with your hands (this is more likely if your kitchen is warm), place the dough in the fridge for 20 minutes to firm it up a bit. Line a 8x4-inch (20x10 cm) or 9x5-inch loaf pan (23x13 cm) with parchment paper, letting the excess hang over the long sides to form a sling. Spread the dough out into the prepared pan and smooth the top out evenly, pressing all the way into corners using your fingers or a flat-bottomed steel cup to get the mixture even on top. Place the pan in the freezer for 30 minutes (or longer) to set. Once chilled, remove from the freezer and using the parchment paper as handles, lift the cookie dough out of the pan. Before removing from the freezer, melt the chocolate.1. Double boiler method: Add a few inches of water to a saucepan and bring to a simmer. Nestle a large heatproof glass bowl that sits on top of the saucepan without touching the water to create a double boiler. Once the water is simmering, add the vegan chocolate chips and coconut oil to the bowl. Whisk frequently with a spatula until the mixture is just melted.2. Microwave method: Add the chocolate and coconut oil to a microwave-safe bowl and microwave on high in 25 to 30-second intervals until the chocolate is almost melted (about 3 intervals). Use a spoon to stir the chocolate until it is melted.
Drizzle the melted chocolate over the cold cookie dough and lightly sprinkle with flaky sea salt, if desired. If the chocolate doesn’t immediately harden, return it to the freezer for 5-10 minutes to set, then slice into 8 thick bars or into smaller squares. Store leftovers in the freezer (they’ll stay good for several weeks).