Line two large, rimmed baking sheets with parchment paper, a silpat liner or lightly grease with cooking spray. Place the oats in a blender or food processor and process until the oats are finely ground.Transfer the oats to a medium bowl. Mix in the flour, baking powder, baking soda, and salt. Set aside.
Using an electric mixer, beat the butter and sugars in a large bowl until fluffy. Beat in the eggs and vanilla. Add the flour mixture and stir just until blended. Stir in the toffee, hazelnuts, and chocolate chips.
Roll the dough into tablespoon-size balls and place them 1-inch apart on the prepared baking sheets. Bake until the cookies are golden, about 12-14 minutes. Cool the cookies on the baking sheets for 5 minutes. Transfer to a cooling rack and cool completely. Repeat the rolling and baking process with the remainder of the dough. Store the cookies tightly covered at room temperature for up to a day or freeze for 1-2 months.
Notes
Toffee: for the toffee candy bar (like Heath bars) finely chopped, you can substitute an equal amount of the toffee bits that are prepackaged by the chocolate chips. Hazelnuts: also called filberts, can often be found in the nuts section but I’ve also found them in the natural foods aisle in bulk containers.