Mix together the flour, baking powder, and salt in a medium-sized mixing bowl.
Blend 1 cup of the oil into the dry ingredients. Stir in just enough water to make a soft dough.
Divide the dough into 4 parts. Roll out 1 part at a time to about 1⁄4" thick. Cut into triangles about 4" long and 2" at their widest.
In a large skillet, heat the remaining peanut oil to about 385°F. Add 3 to 4 pieces of dough at a time. Stir the oil until the sopapillas puff up like pillows. Fry until light brown. Lay on paper towels to drain off excess grease.
Chop the pineapple into 1⁄2" pieces. Drain off juice. Heat the pineapple to lukewarm in a small saucepan over medium-low heat, about 2–4 minutes.
Open a small hole in the side of each sopapilla and spoon about 2 tablespoons of pineapple inside it.
Mix together the cinnamon and sugar in a bowl. Sprinkle on the top of each sopapilla.