In a food processor, blitz the oats and almonds until finely ground. Transfer to a large bowl and add the rest of the base ingredients. Mix well and press evenly into the prepared tin.
Melt the chocolate in the microwave in 10-second bursts until smooth. Stir in the peanut butter, then pour over the base. Gently tap the tin to remove any air bubbles.
Refrigerate for 1-2 hours until firm.
Slice into bars and enjoy. Store in the fridge in a sealed container for 1-2 weeks.