For the raisin filling mix the raisins, sugar, cornstarch, water and lemon juice.
Cook stirring constantly over low heat until thickened about 5 minutes. Cool.
For the crumb mixture. Mix butter with sugar, add dry ingredients, then mix in the oat. Mix well.
Press half of the crumb mixture into greased 13x 9x 2 pan.
Spread the raisin filling over the pressed on crumb mixture.
Pat on remaining crumb mixture on top of filling.
Bake at 400 degrees 20 to 30 minutes.