Preheat oven to 400 degrees F. Spray muffin tin with cooking spray.
In a large bowl, stir together condensed milk, egg, and vegetable oil until smooth. Add baking mix, and stir just until flour is mixed in. Fold in pineapple just to incorporate into dough. (Don’t over stir.)
Fill muffin tins about 2/3 full, and bake in preheated oven for 18-22 minutes, until golden brown and toothpick inserted into the center of the largest muffin comes out dry. Cool slightly before serving.