1. Adjust the oven racks to the low and middle positions and heat the oven to 350 degrees. Line 2 large baking sheets with parchment paper or spray them with nonstick cooking spray.
2. Whisk the flour, baking powder, and salt together in a medium bowl.
3. Either by hand or with an electric mixer, beat the butter on medium speed until creamy. Add the sugars; beat until fluffy, about 3 minutes. Beat in the eggs, 1 at a time.
4. Stir the dry ingredients into the butter-sugar mixture with a wooden spoon or large rubber spatula. Stir in the oats, candy, and chips.
5. Working with a generous 2 Tablespoons of dough each time, roll the dough into 2-inch balls. Place the balls on the prepared baking sheets, spacing them at least 2 inches apart.
6. Bake until the cookie edges turn golden brown, 22 to 25 minutes, rotating the baking sheets front to back and top to bottom halfway through the baking time. Let the cookies cool on the baking sheets for 2 minutes. Transfer the cookies with a wide metal spatula to a wire rack. Let cool at least 30 minutes.