Line the pan: Line an 8x8-inch pan with parchment, leaving overhang on two sides for easy lifting.
Warm the base: In a medium saucepan over low heat (or in a microwave-safe bowl in 20–30 second bursts), gently melt 1/2 cup coconut oil (or butter) with 3/4 cup peanut butter and 1/2 cup honey.
Stir until smooth and glossy. Remove from heat and stir in 1 teaspoon vanilla and 1/2 teaspoon fine sea salt.
Add the oats: Stir in 3 cups rolled oats until fully coated. If using add-ins like 2 tablespoons chia seeds or 1/4 cup shredded coconut, fold them in now.
Press the base: Transfer the mixture to the lined pan.
Use a spatula or the back of a measuring cup to press it down firmly and evenly into the corners. Firm pressing = bars that hold together.
Make the chocolate layer: Melt 1 cup chocolate chips with 1 tablespoon coconut oil using low heat or short microwave bursts, stirring until smooth.
Top and smooth: Pour the melted chocolate over the oat base and spread into an even layer. If you like, sprinkle flaky sea salt, chopped nuts, or crushed pretzels on top.
Chill: Refrigerate for at least 1–2 hours, or until the chocolate is set and the base is firm.
Slice and serve: Lift the slab out using the parchment. Warm a sharp knife under hot water, dry, and cut into 12–16 bars.
Store as directed below.