Line a 9-inch square metal baking pan with a 12- to 14-inch-long sheet of foil, letting excess hang over sides, and butter foil in pan.
Toss together oats, flour, brown sugar, chips, coconut, baking powder, and salt in a large bowl. Beat together butter, egg, and vanilla with a fork in another bowl, then stir into oat mixture until incorporated. Spoon batter into baking pan, patting evenly.
Bake in middle of oven until set, about 25 minutes. Remove from pan by lifting ends of foil. Cool on a rack, then cut into 16 squares.
